GUAC-888: Init socket last_write_timestamp during alloc, otherwise keep-alive math fails until data has been written, which may result in the keep-alive never being sent.
GUAC-935: Only update display size if it's been longer than 250ms.
GUAC-935: Add missing headers. Fix test for PubSub.
GUAC-935: Document parameters of newly-added functions.
Merge pull request #4 from glyptodon/limit-resize-freq

GUAC-935: Only update display size if it's been longer than 250ms.
Merge branch 'master' into rdp-sharing-support

Conflicts:
	src/libguac/socket.c
	src/protocols/rdp/client.c
	src/protocols/rdp/client.h
	src/protocols/rdp/guac_handlers.c
	src/protocols/rdp/rdp_disp.c