src: Compile defaltehd and inflatehd with c++

This commit also fixes defaltehd always reports output length is 0.
Share stream_group weight among streams marked as top
Adjust weight when pushing data to queue
src: Output debug data in GOAWAY in printable ascii

Non printable ascii is printed as ".".
Implement ALTSVC frame
Check payload length when submitting GOAWAY and ALTSVC
Rename framebuflen as framerv, cause it is not a length
Make group weight range [1, 256], inclusive

We do -+1 on serialization and deserialization since the field is 1
byte.  This change also parameterized range so that we can change it
easily.
Add flags to nghttp2_nv structure

This is preliminary change for upcoming HPACK updates.  The flags are
used to determine the name/value pair is indexable or not.
Fix compile error with --enable-werror
Honor NGHTTP2_NV_FLAG_NO_INDEX in deflater and inflater
Update static table
Update huffman codes
Add flags parameter to nghttp2_on_header_callback
python: Update according to HPACK change, but flags are not used yet