Implement simplified dependency based priority
Allow exclusive dependency to stream 0
priority: Add tests
Distribute effective weight among only streams with marked as top

If stream with dpri value of no_data, we check any its descendant has
stream with dpri value of top.  If so, we have to distribute of its
portion of weight to its descendants.
Handle circular dependency

Handle the situation if a stream is told to depend on its descendant.
This is what
http://tools.ietf.org/html/draft-ietf-httpbis-http2-12#section-5.3.3
says.
Merge branch 'priority'
Implement BLOCKED frame
Implement compressed DATA

The library interface supports compressed DATA.  The library does not
deflate nor inflate data payload.  When sending data, an application
has to compress data and set NGHTTP2_DATA_FLAG_COMPRESSED to
data_flags parameter in nghttp2_data_source_read_callback.  On
receiving, flags parameter in nghttp2_on_data_chunk_recv_callback
includes NGHTTP2_FLAG_COMPRESSED.  An application should check the
flags and inflate data as necessary.  Since compression context is per
frame, when DATA is seen in nghttp2_on_frame_recv_callback, an
application should reset compression context.
Declare h2-12 for now
Update README.rst