[WIP] Bus implementation

[dmcgowan]

Implementation of a bus using libchan to pass messages. There is a simple registration and message model to facilitate routing messages to clients connected to the bus. The design and implementation is in progress as this is just a prototype. There is also a higher level plugin interface being prototyped using this but not included in this PR.

[dmcgowan]

Right now the NewClient function probably does more than it should since it creates the libchan spdy-based transport from the net.Conn (normal libchan usage), then initializes with the bus across that transport. Perhaps a rename or hiding Client behind an interface would be less confusing.

// NewClient creates a new libchan transport using the
// provided connection and initializes the transport
// with the bus.

[dmcgowan]

Added a Readme to libchan/bus to better explain what bus is trying to achieve the design goals around it

[dmcgowan]

Updated interface to add a local client which attaches directly to the bus without the need for going through a network connection.

[dmcgowan]

Moved to https://github.com/dmcgowan/libchan-hack