Move to stable API

[Matthiee]

Stable API

Move towards stable API provided by FMP.

See https://site.financialmodelingprep.com/developer/docs/stable

Plan

• [ ] Create new v1 base branch
  • Update readme to reflect the API being used
• [ ] Convert all endpoints to the new stable
• [ ] Move to correct categories #137
• [ ] Create long-lived legacy branch (for hotfixes)
• [ ] Release v1