Fantam

1. Start with Bob Nystrom's Bantam.
2. Port to F# and flip the expression problem around.
3. ????
4. Profit!

Most contemporaryPratt parserexamples use the OO style. I wanted to see what it looks like in a purely funtional style. The code isn't as tidy as I'd like yet, but the tests pass, and I'll work on cleaning it up as I get time.