rename transformation commands to keep them consistent.

[vlandham]

I should have made this a PR - but wasn't thinking, so I can revert if needed. The latest 0.2.0 release renames some of the transformation functions, to keep more in line with our tokens2counts and tokens2pos commands.

Specifically:

• lowercase has become tokens2lower
• uppercase has become tokens2upper
• stem has become tokens2stem
• topbigrams has become tokens2topbigrams

This keeps them all contained together in the --help documentation, and makes it more clear what content they are expecting. The tradeoff is they are slightly more verbose.

Thoughts @iros / @arnicas ?

changed in 2685e9425e092ccb7fb39e428d0304249b33e144

[iros]

Sorry +1