Update stream open and replies

Separating create and open allows for easier avoidance of race conditions between saving a stream reference and receiving a reply.
Replies are now controlled by the handlers instead of automatically sending after a stream frame.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Fix race conditions accessing stream map and framer

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Add frame handling priority

Closes #7

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)