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 Update API categories to align with documentation again #137
• Create long-lived legacy branch (for hotfixes)
• Release v1