Jort

* Add single line checkpoints
* Rename `Checkpoint` object to more appropriate `Block`
* Change config initialization
* Remove automatic side effects

* Add docs for database operations
* Add `to_db` to function decorators

* Update CLI using `click`
* Command groups, including `jort config` and `jort track`
* `jort track` automatically discerns commands from PIDs

* Implement email callback
* Custom exceptions

* `time_func` -> `track`
* Improve decorator syntax, including callback support