Update Docs with Finalize Block (cometbft#760)

The PR closes issue #25 partially. 

Changes made:
- Bump version v0.37 to v0.38 in docs.
- Update docs to remove reference to `BeginBlock`, `EndBlock`, and `DeliverTx` and consolidate them into `FinalizeBlock.`
- Minor changes to the formatting of docs.

#### PR checklist

- [ ] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use [unclog](https://github.com/informalsystems/unclog) to manage our changelog)
- [X] Updated relevant documentation (`docs/` or `spec/`) and code comments