Add go.net spdy library as subpackage.

Going to be doing some memory management changes to it soon. Easier
to fork than to submit upstream for now.
Add InDataFrame
Buffer up to receive window on frame read.

This is obvious in hindsight, but I should have been using the
windowing functionality to actually window according to my internal
buffer.
Remove buffer preallocation.

No need to have the buffer as a pointer.

Also size buffer on receive window. For most cases, we'll never hit
the receive window and we can save the memory while avoiding the
piecemeal allocation that would happen if we grew on frame sizes.
Merge branch 'framing'

This moves a fork of the go.net spdy package into this repo. This
allows for better memory management and receive window handling.

Many thanks to the contributers to go.net for providing me with this
base to work on top of.

Conflicts:
	server_test.go
	session.go
	stream.go