- Completed implementation of /beacon/head
- renamed 'latest_finalized_checkpoint' to 'current_finalized_checkpoint' for consistency
- Reorganised list of endpoints in both spec & router so that they match
- Fixed the content-type modifications for /metrics
- Added a new 'RFC' tag to the spec, to tag things that we have not implemented and aren't sure if it's useful.
- Moved 'deposit_contract' under /spec