Adds git `tagreflog` and `untagreflog`

Tags the last N (default all) reflog entries as `reflog-#`.
Adds git `pr` = pull request

- copies logs to clipboard
- opens GitHub pull request URL

TODO: currently requires an `against` (branch to pull into) argument
Allows specifying `current` branch to `git pr`
Updates `git pr` for new GitHub URL

Slashes in branch names are no longer converted to semicolons.
Adds basic PostgreSQL `.psqlrc`