Add connection.blocked, connection.unblocked

Following the [json
spec](http://hg.rabbitmq.com/rabbitmq-codegen/file/tip/amqp-rabbitmq-0.9.1.json#l153)
add these two methods.  The client needs to advertise support in the
connection extensions for these methods to be sent.
connection.blocked & connection.unblocked

RabbitMQ delivers this method when it activates and deactivates TCP
pushback on all connections due to a limited global resource.
Restrict table field value types

In order to be compatible with other clients, and RabbitMQ server at
version 3.1, only encode and decode types supported by the majority of
clients.

Ref #61
Go 1.0.3 compat
Document type assertion and int32 expectation
Merge pull request #61 from streadway/61-field-types

Audit other server and client field value types
Ignore the specification compiler during builds
Panic on unlikely new frame types
Correct generated isSoftExceptionCode

A little bit of C slipped through where a fallthrough is implicit.  This
should have read:

```
switch {
  case A:
    fallthrough
  case B:
    fallthrough
  case C:
    return true
}
```
Ignore all command outputs
Test under multiple go versions
Merge pull request #75 from streadway/75-connection.blocked

Support connection.blocked (coming in RabbitMQ 3.2)
Simplify table lookup

Leverage nil maps and checked type assertions returning zero values.
Report closing error, if any
Link to RabbitMQ tutorials ported to Go
add test to repro #84
Move channel field mutex from reentrant 'send'

IO errors from send can call shutdown on the connection
which calls shutdown on the channel which tries to claim a lock that is
held by the Publish that initiated the send.

The field mutex `m` doesn't need to lock any access before the send,
only the publish counter and publisher confirm heap so only include
those fields in the critical section.

Thanks @alexzorin
Increase the deadlock timeout for travis.
README: update link to documentation
Merge pull request #85 from garyburd/patch-1

README: update link to documentation