Migrated val_t and ci_esc to common header.
Rewrapped a code block.
Abandoned multi-phase trie decoding.
Bashed a few superfluous includes.

Originally, quite a few places derived directly from event_handler_c.
After replacing most of these with mocks, I forgot to fixup some
includes. These are now corrected.
Added forwards for decoders.
Added unrecog decoder, unit test.
Small const-correctness fix.
Decoder chain no longer implicitly fires unrecog if decoding fails.