Introduce ThreadDeathWatcher

Motivation:

PooledByteBufAllocator's thread local cache and
ReferenceCountUtil.releaseLater() are in need of a way to run an
arbitrary logic when a certain thread is terminated.

Modifications:

- Add ThreadDeathWatcher, which spawns a low-priority daemon thread
  that watches a list of threads periodically (every second) and
  invokes the specified tasks when the associated threads are not alive
  anymore
  - Start-stop logic based on CAS operation proposed by @tea-dragon
- Add debug-level log messages to see if ThreadDeathWatcher works

Result:

- Fixes #2519 because we don't use GlobalEventExecutor anymore
- Cleaner code
Use Java 5 foreach for arrays for brevity at no cost
Fix checkstyle
Add awaitInactivity() to GlobalEventExecutor and ThreadDeathWatcher

Motivation:

When running Netty on a container environment, the container will often
complain about the lingering threads such as the worker threads of
ThreadDeathWatcher and GlobalEventExecutor.  We should provide an
operation that allows a use to wait until such threads are terminated.

Modifications:

- Add awaitInactivity()
- (misc) Fix typo in GlobalEventExecutorTest
- (misc) Port ThreadDeathWatch's CAS-based thread life cycle management
  to GlobalEventExecutor

Result:

- Fixes #2084
- Less overhead on task submission of GlobalEventExecutor
Fix checkstyle
[#2494] Fix data curruption by ChannelTrafficShapingHandler

Motivation:
ChannelTrafficShapingHandler may corrupt inbound data stream by
scheduling the fireChannelRead event.

Modification:
Always call fireChannelRead(...) and only suspend reads after it

Result:
No more data corruption
OkResponseHandler should return a FullHttpResponse.

Motivation:
Currently OkResponseHandler returns a DefaultHttpResponse which is not
correct and it should be returning complete http response.

Modifications:
Updated OkResponseHandler to return an instance of
DefaultFullHttpResponse.

Result:
It is not possible to add compression to the example without getting any
errors.
ChannelFlushPromiseNotifier should allow long value for pendingDataSize

Motivation:
At the moment ChannelFlushPromiseNotifier.add(....) takes an int value for pendingDataSize, which may be too small as a user may need to use a long. This can for example be useful when a user writes a FileRegion etc. Beside this the notify* method names are kind of missleading as these should not contain *Future* because it is about ChannelPromises.

Modification:
Alter add(...) method to take a long for pendingDataSize. Rename all *Future* methods to have *Promise* in the method name to better reflect usage.

Result:
ChannelFlushPromiseNotifier can be used with bigger data.
Require Maven 3.1.1 or above

.. because the build fails with an older Maven version due to Eclipse
Aether issues
Clean up MpscLinkedQueue, fix its leak, and make it work without Unsafe

Motivation:

MpscLinkedQueue has various issues:
- It does not work without sun.misc.Unsafe.
- Some field names are confusing.
  - Node.tail does not refer to the tail node really.
  - The tail node is the starting point of iteration. I think the tail
    node should be the head node and vice versa to reduce confusion.
- Some important methods are not implemented (e.g. iterator())
- Not serializable
- Potential false cache sharing problem due to lack of padding
- MpscLinkedQueue extends AtomicReference and thus exposes various
  operations that mutates the internal state of the queue directly.

Modifications:

- Use AtomicReferenceFieldUpdater wherever possible so that we do not
  use Unsafe directly. (e.g. use lazySet() instead of putOrderedObject)
- Extend AbstractQueue to implement most operations
- Implement serialization and iterator()
- Rename tail to head and head to tail to reduce confusion.
- Rename Node.tail to Node.next.
- Fix a leak where the references in the removed head are not cleared
  properly.
- Add Node.clearMaybe() method so that the value of the new head node
  is cleared if possible.
- Add some comments for my own educational purposes
- Add padding to the head node
  - Add FullyPaddedReference and RightPaddedReference for future reuse
- Make MpscLinkedQueue package-local so that a user cannot access the
  dangerous yet public operations exposed by the superclass.
  - MpscLinkedQueue.Node becomes MpscLinkedQueueNode, a top level class

Result:

- It's more like a drop-in replacement of ConcurrentLinkedQueue for the
  MPSC case.
- Works without sun.misc.Unsafe
- Code potentially easier to understand
- Fixed leak (related: #2372)
Initial STOMP protocol work from @sskachkov
Overall refactoring of the STOMP codec

- StompObject -> StompSubframe
- StompFrame -> StompHeadersSubframe
- StompContent -> StompContntSubframe
- FullStompFrame -> StompFrame
- StompEncoder/Decoder -> StompSubframeEncoder/Decoder
- StompAggregator -> StompSubframeAggregator
- Simplify the example
- Update Javadoc
- Miscellaneous cleanup
Introduce MessageAggregator and DecoderResultProvider

Motivation:

We have different message aggregator implementations for different
protocols, but they are very similar with each other.  They all stems
from HttpObjectAggregator.  If we provide an abstract class that provide
generic message aggregation functionality, we will remove their code
duplication.

Modifications:

- Add MessageAggregator which provides generic message aggregation
- Reimplement all existing aggregators using MessageAggregator
- Add DecoderResultProvider interface and extend it wherever possible so
  that MessageAggregator respects the state of the decoded message

Result:

Less code duplication
Fix StompSubframeEncoderTest failure

Motivation:

StompSubframeEncoderTest fails because StompHeaders does not respect the order of the headers set.

Modifications:

Use LinkedHashMap instead of HashMap

Result:

Fixes test failures
[#2436] Unsafe*ByteBuf implementation should only invert bytes if ByteOrder differ from native ByteOrder

Motivation:
Our Unsafe*ByteBuf implementation always invert bytes when the native ByteOrder is LITTLE_ENDIAN (this is true on intel), even when the user calls order(ByteOrder.LITTLE_ENDIAN). This is not optimal for performance reasons as the user should be able to set the ByteOrder to LITTLE_ENDIAN and so write bytes without the extra inverting.

Modification:
- Introduce a new special SwappedByteBuf (called UnsafeDirectSwappedByteBuf) that is used by all the Unsafe*ByteBuf implementation and allows to write without inverting the bytes.
- Add benchmark
- Upgrade jmh to 0.8

Result:
The user is be able to get the max performance even on servers that have ByteOrder.LITTLE_ENDIAN as their native ByteOrder.
Reducing memory usage for HTTP/2

Motivation:

The connection, priority tree, and inbound/outbound flow controllers
each maintain a separate map for stream information. This is wasteful
and complicates the design since as streams are added/removed, multiple
structures have to be updated.

Modifications:

- Merging the priority tree into Http2Connection. Then we can use
Http2Connection as the central stream repository.

- Adding observer pattern to Http2Connection so flow controllers can be
told when a new stream is created, closed, etc.

- Adding properties for inboundFlow/outboundFlow state to Http2Stream.
This allows the controller to access flow control state directly from
the stream without requiring additional structures.

- Separate out the StreamRemovalPolicy and created a "default"
implementation that runs periodic garbage collection.  This used to be
internal to the outbound flow controller, but I think it is more general
than that.

Result:

HTTP/2 classes will require less storage for new streams.
[#2544] Correctly parse Multipart-mixed POST HTTP request in case of entity ends with odd number of 0x0D

Motivation:
When an attribute is ending with an odd number of CR (0x0D), the decoder
add an extra CR in the decoded attribute and should not.

Modifications:
Each time a CR is detected, the next byte was tested to be LF or not. If
not, in a number of places, the CR byte was lost while it should not be.
When a CR is detected, if the next byte is not LF, the CR byte should be
saved as the position point to the next byte (not LF). When a CR is
detected, if there is not yet other available bytes, the position is
reset to the position of CR (since a LF could follow).

A new Junit test case is added, using DECODER and variable number of CR
in the final attribute (testMultipartCodecWithCRasEndOfAttribute).

Result:
The attribute is now correctly decoded with the right number of CR
ending bytes.
[#2542] HTTP post request decoder does not support quoted boundaries

Motivation:
According to RFC2616 section 19, boundary string could be quoted, but
currently the PostRequestDecoder does not support it while it should.

Modifications:
Once the boundary is found, one check is made to verify if the boundary
is "quoted", and if so, it is "unqoted".

Note: in following usage of this boundary (as delimiter), quote seems no
more allowed according to the same RFC, so the reason that only the
boundary definition is corrected.

Result:
Now the boundary could be whatever quoted or not. A Junit test case
checks it.
Pluggable algorithm to choose next EventLoop

Motivation:

Currently when a new event loop is needed to register a channel our EventLoopGroup implementations just
use a round-robin like algorithm to choose the next event loop. Unfortunately this is not always good
enough as different event loops may become more busy than others over time. This is especially true when
an application handles different kinds of connections (long-living and short-living). This change allows
developers to plug in their own algorithms to choose the next event loop and to collect metrics about the
busyness of the event loops. See #1230

Modifications:

- TODO

Result:

- Developers can plug in their own algorithms into MultithreadEventLoopGroup constructors.
- Developers can gather metrics/feedback from the event loops and use the data in their custom algorithms.