Use a map to avoid gsub on every parse pattern

[jmondo]

Same idea as #340 except less intrusive to the developer

I borrowed from active support #underscore method for snake casing

[davispuh]

I've been working on #278 (which rewrites quite a bit of logic) for some while but it's still unfinished and lately I haven't had time to continue it but I still plan on finishing it eventually and you should look at it since it doesn't need this at all...