REORG: include: move hpack*.h to haproxy/ and split hpack-tbl

REORG: include: move hpack*.h to haproxy/ and split hpack-tbl

The various hpack files are self-contained, but hpack-tbl was one of
those showing difficulties when pools were added because that began
to add quite some dependencies. Now when built in standalone mode,
it still uses the bare minimum pool definitions and doesn't require
to know the prototypes anymore when only the structures are needed.
Thus the files were moved verbatim except for hpack-tbl which was
split between types and prototypes.