Now that we only have one Repository implementation, no need for the
command-line options to choose it either. I'm removing these as a separate
commit to show what we will need to do if we add another Repository
implementation in the future (even though I don't foresee us doing that
any time soon)
The layered storage format is good enough that we don't need the rocksdb
implementation anymore. There are a lot of known issues but we'll keep
working on them.
- Move source tree overview into separate docs/sourcetree.md and update it.
- Add glossary: docs/glossary.md
- Add a draft of Architecture overview to main Readme.md
