string_bytes: add StringBytes::IsValidString()

Performs a quick, non-exhaustive check on the input string to see if
it's compatible with the specified string encoding.

Curently it only checks that hex strings have a length that is a
multiple of two.
crypto: fix assert() on malformed hex input

Use the StringBytes::IsValidString() function introduced in commit
dce26cc to ensure that the input string meets the expectations of the
other StringBytes functions before processing it further.

Fixes the following assertion:

    Assertion failed: (str->Length() % 2 == 0 && "invalid hex string
    length"), function StorageSize, file ../../src/string_bytes.cc,
    line 301.

Fixes #5725.
docs: Warning about consuming response
http: improve chunked res.write(buf) performance

Avoid a costly buffer-to-string operation. Instead, allocate a new
buffer, copy the chunk header and data into it and send that.

The speed difference is negligible on small payloads but it really
shines with larger (10+ kB) chunks. benchmark/http/end-vs-write-end
with 64 kB chunks gives 45-50% higher throughput. With 1 MB chunks,
the difference is a staggering 590%.

Of course, YMMV will vary with real workloads and networks but this
commit should have a positive impact on CPU and memory consumption.

Big kudos to Wyatt Preul (@wpreul) for reporting the issue and providing
the initial patch.

Fixes #5941 and #5944.
node: add inTick and lastThrew to infoBox

To prevent all unnecessary calls to JS from MakeCallback, the remaining
two immediate return variables inTick and lastThrew have been added to
infoBox. Now MakeCallback should never need to call into JS unless it
absolutely has to.

Also removed Tock. Performance tests showed it was at least as fast or
faster than using a normal object, and this is more readable.
cpplint: make lint rules closer to node's source

* Support C-style header guards (/* comments */)
* Support `class NODE_EXTERN something`
* Support `}  // extern "C"` closures
* Ignore header order
* Ignore `long/short` usage (because of OpenSSL's API)
src: lint c++ code
make: add `cpplint` to `test` target

Also, exclude some C-headers, machine generated headers and tweaked
sources from cpplint file list.
etw_provider: unbreak windows build
doc: remove travis status image

The project has moved to Jenkins. The status image is no longer
needed and perpetually shows a failed build. Remove it.
tools: cpplint: fix up build/include_order rule

Change the build/include_order rule to match our preference:
project headers before system headers.

The rationale is that system headers before project headers makes it
easy to slip in bugs where a project header that requires a definition
from a system header, forgets to include the system header but still
compiles because the source files that include the project header
coincidentally include the system header too.

A good example is the size_t type. A project header file that needs the
definition of size_t should include stddef.h but forgetting to do so
will probably go unnoticed for a long time because almost every other
system header includes stddef.h (either directly or indirectly) and
almost every source file includes one or more system headers.

Ergo, project headers before system headers. It's a good thing.
src: more lint after cpplint tightening

Commit 847c6d9 adds a 'project headers before system headers' check
to cpplint. Update the files in src/ to make the linter pass again.
build: un-break the windows build
build: disable some msvc compiler warnings

These are not real problems, and they are so plenty that actual problems
are hidden from view.
src: don't include <string.h> twice in src/node.cc
cpplint: exclude src/node_win32_perfctr_provider.cc

It's forced to violate the build/include_order rule because it includes
a header file generated with ctrpp.exe that doesn't include perflib.h
itself.
os: add mac address to networkInterfaces() output
tls_wrap: parse tls session ticket extension

And, if present and non-empty, don't invoke `resumeSession` callback.

fix #5872
events: fix memory leak, don't leak event names

Before this commit, events were set to undefined rather than deleted
from the EventEmitter's backing dictionary for performance reasons:
`delete obj.key` causes a transition of the dictionary's hidden class
and that can be costly.

Unfortunately, that introduces a memory leak when many events are added
and then removed again. The strings containing the event names are never
reclaimed by the garbage collector because they remain part of the
dictionary.

That's why this commit makes EventEmitter delete events again. This
effectively reverts commit 0397223.

Fixes #5970.
test: fix pummel/test-net-connect-memleak

* Run the garbage collector before creating the big array. It doesn't
  matter now but if in the future something in node.js core creates
  a lot of reclaimable garbage, that will break the test's expectation.

* The first RSS check was being done too late. The garbage collector
  might have run before the check, throwing off the 'reclaimed memory'
  calculation.

* Due to changes in how V8 represents the big array internally, the
  actual memory usage is just below 256 MB on x64. Update the test's
  expectation.