Todi

Added
- New feature: Import and Export todi databases.
- Import from anywhere, by indicating the path of the backup file.
- Backup files are exported to `~/todi_backups/` directory.

Fixed
- Missing docstrings.
- Removed docstrings from help messages.

Changed
- Database directory is now `~/.todi/`.

Added
- CHANGELOG file.

Fixed
- `Todi` has being creating the db directory on every directory it was being called from. Causing that sometimes, there was ***no pending tasks***.
- From now on, the database directory will be created on `home/`.
- Type hint errors detected by `mypy`.

Changed
- Database directory was modified to keep it hidden and identified.
- Created a new directory `.todi/`, to storage the database.
- The old directory `db/`, will not be deleted or modified.
- The database will be moved from `db/` to `.todi/`.

Created
- **Todi**, a command line tool to manage to-do tasks.
- `List`, `Add`, `Update` and `Delete` tasks.
- Change status: `TODO` (default), `DOING` and `DONE`.
- `Clean` command to remove `DONE` tasks.