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.
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
Merge pull request #80 from michaelklishin/patch-1

Link to RabbitMQ tutorials ported to Go
Documentation related wording
Allow providing connection config to DialTLSWithConfig
Document non-goals

Fixes #81
List formatting
DialConfig parameterizes connection config

No more magic contructors left during transport setup.  This should be
simpler instead of requiring the application to setup the transport then
use Open(rwc, config).
Merge remote-tracking branch 'torkale/dial_config' into 86-dial-config

Alternative implementation to torkale/dial_config

Conflicts:
	connection.go
Documentation of Config

Now that Config works for both Dial and Open, some of the fields have
picked up defaults from the Dial path.
Minor grammar/typo nits