Retreive Pallet API documentation from Frequency

[wilwade]

Goal: Nice docs that are focused on developers using the chain, not docs for Rust developers

How: Custom Readmes per Frequency Pallet that are structured to also be pulled into these docs

• [x] Templates & Examples
• [x] Capacity https://github.com/frequency-chain/frequency/pull/1997
• [x] Frequency TX Payment https://github.com/frequency-chain/frequency/pull/1990
• [x] Handles https://github.com/frequency-chain/frequency/pull/1984
• [x] Messages https://github.com/frequency-chain/frequency/pull/1981
• [x] MSA https://github.com/frequency-chain/frequency/pull/1962
• [x] Schemas https://github.com/frequency-chain/frequency/pull/1968
• [x] Stateful Storage https://github.com/frequency-chain/frequency/pull/1989
• [x] Time Release https://github.com/frequency-chain/frequency/pull/1998
• [ ] Add remaining cross links

Generalized Pieces

(Check off once added to ^ not when complete)

• [ ] Pallet Errors
  • [ ] Frequency
  • [ ] Substrate
• [ ] Pallet Extrinsics
  • [x] Frequency
  • [ ] Substrate
• [ ] Pallet State Queries
  • [x] Frequency
  • [ ] Substrate
• [ ] Runtime RPCs
  • [ ] Frequency
  • [ ] Substrate
• [ ] Node RPCs
  • [x] Frequency
  • [ ] Substrate

Old Ideas

• Using the new cargo rustdoc nightly unstable option of --format-output json + something like https://github.com/IonicaBizau/json2md