Revert a change that caused WINDOW_UPDATE frames to be sent on closed streams
Test receiving an unexpected frame on a stream
Merge pull request #39 from alekstorm/header-decoding-order

Refactor Stream to ensure header blocks are decoded in the correct order
Remove HTTP20Response object.
Implement server push, exposed as the HTTP20Push and HTTP20PushedResponse classes
Rename extract_from_key_value_set to pop_from_key_value_set, have it modify the set in-place
Temporarily revert addition of 'pushed' attribute from requests adapter Response object pending further discussion
Merge BaseHTTP20Response, HTTP20Response, and HTTP20PushedResponse for simplicity
Add more comments to critical paths in Stream