First release.
Features:
- init config with `sample-config` command.
- provide custom config flag with `invoicepy -C`, default `~/.pyconfig.json`
- print invoice pdf with `pdf` command.
- invoices are saved to user config file (this can be disabled with `--no-save` option).
- increment invoice number based on `series` field for given company based on saved invoices.
- companies and customers can be saved configured with alias for quick access when creating new invoices.
- simple template is provided, user can add their own templates with `custom_templates_dir` option. (`-t` flag)
- open generated invoice in browser with `-b` flag.
- support for vat lines, simple calculations are done to calculate tax amounts.