Use substitution indexing

Fix a bug with the opcodes.
Use new code in test file
Display contexts
Fix bug with max size handling
Remove obsolete files
Fix bug with negative indices in the reference set
Keep track of whether the round-tripped header set equals the original
Display headers in pseudo-HTTP format
Rearrange layout
More layout rearrangement
Sort headers when converting to string
Tweak header-parsing regexp
Update README
Follow header emission rules
Fix duplicate header bug
Use a better string escaping mechanism
Compare contexts
Make HeaderDecoder stream its emitted headers
Implement changing the header table max size
Handle edge cases related to the header table max size being exceeded