feat: Create programmatic API

[epage]

TODO

• Determine how file_id_ref should be handled
• Clarify intent on what parts of the API for meant for external use or not

Added spell_check_str

• Doesn't requie file to be on disk
• Does not read stdin or write to stdout
• Acts as an iterator in the report-only use case
• Acts as a coroutine in the auto-apply use case

Fixes #29

BREAKING CHANGE: spell_check_tokens API changed

[epage]

Determine how file_id_ref should be handled

When digging into the code, I could not see what impact mutating file_id_ref has.

Clarify intent on what parts of the API for meant for external use or not

Proposal:

• __init__ continues to expose spell_check_str and everything needed to run it
• Create cli.py
  • Move main and everything else not listed above into here
  • Add a _ prefix to all of these symbols to clarify intent of no one else using it.