support OR in data.yml computed fields, allowing for more than 2 operands

[ultrasaurus]

so we could do something like:

  academics.program.assoc:
    calculate: CIP49ASSOC or CIP54ASSOC or CIP12ASSOC or CIP33ASSOC
    type: boolean

this is needed to address: RTICWDT/college-scorecard#951

[ultrasaurus]

FYI: I'm working on this. I experimented with https://github.com/rubysolo/dentaku -- but it wasn't a good fit since Ruby evaluates 0 to true, and also our symbols are case-sensitive. I've got something working using https://github.com/kschiess/parslet which seems to work quite well, producing clean and robust code that is easily extensible.

I'm still doing some local testing, but I updated RTICWDT/college-scorecard#951 with modified query proposal and emailed ED some data generated from those queries from college scorecard data.