Buffer Pooling

[niaow]

This is a continuation of gorilla#9. The general idea was to create an interface implemented by sync.Pool which could be used to manage write buffers.

[niaow]

The previous implementation attempt was here: https://github.com/y3llowcake/websocket/tree/gb_buffers.

[niaow]

I git cherry-picked the commit from gb_buffers onto current master. It compiles, but there is currently a panic. I expected that changes in the code would cause something. I am investigating.