Tsks

Implemented
* the `-t` flag to act on tasks due (adding, editing or listing today's tasks)

Enhanced
* Actions are now called without double flags (e.g. `tsks init`).
See [the documentation](README.md) for more details

Fixes
* `updated_at` now receives the current timestamp when ending or editing a task

Implemented
* installable from PyPI using pip
* the `--help` and `--version` arguments to usage informations
* the `--init` and `--uninstall` to create/remove the storage
* the `--add`, `--done`, `--edit`, and `--remove` arguments to enter/manipulate tasks
* the `--list` and `--archive` to see current active/done tasks
* the `--clear` to reset the storage to be empty