Accept keywords and variable names in lowercase

[willisblackburn]

Complications:

1. Don't know if the platform supports lowercase.
2. There's currently no way in the parser to convert to uppercase.

Probably there's a "caps lock" flag in the parser that we can turn on or off with a PVM command. Every time we read a byte, if it's lowercase and caps lock is set, we convert it to uppercase before doing anything with it.