Add instrument methods, docs, and tests

[patking02]

• [x] Export Instruments (Data Entry Forms)
• [x] Export PDF file of Instruments
• [x] Import Instrument-Event Mappings

[pwildenhain]

Are you planning to make this addition as well? Or are you just documenting the parts of the API that we're still missing?

[patking02]

Yes, working on a PR now!