Micro-library to serialize and deserialize ris files. WIP.

note to self:

broad strategy:

• enum with two types, multi-tag with associated types string for label and array for elements; single tag with associated types string and content.
• parse by initializing a map of multi-tags and a map of single tags, looping over lines, for each line:
  • extract tag and content
  • test tag against list of tags, fail the whole thing if not valid.
  • test content against any validator for tag, fail the whole thing if not valid
  • if content in multi-list, check to see if exists in multi-tag map, if so, append to inner list, if not, create list with element
  • if content in single-tag-list, check to see if in there already, if so, impermissible dupe and fail; if not, add.
• then create a codable struct from those maps. in the initializer, handle parsing out into subfields, date types, etc.
• then it should be able to dump to json, and should be easy-ish to reverse this to serialize to a ris.