Normalize WordDB.new usage.
Move some duplicated lines to the load_files method.
Conjugations and derivations are now morphological rules that share certain attributes and lookup characteristics, as are past participles and gerunds, which are no longer hardcoded in the structure code. Default mophological rule code is now in Lexicon classes rather than in structure. Regular verb conjugations are added in the parser as fully-fledged lexemes. Progressive auxiliaries are correct now.
Remove debug code, conjugate via fallback instead of dying in some places, and switch @lexemes to a hash for speed.