Add ability to import Tristan v2 data

[bcaddy]

• [x] New backend for loading data that supports Tristan v1
• [x] Tristan v2 support
  • [x] fields
  • [x] params
  • [x] particles
  • [x] spectra

[bcaddy]

PR #9 should be addressing everything except Tristan v2 spectra when it is complete

[bcaddy]

PR #20 completes this