Psrqpy

- Allow `PMTOT_ERR` value to be extracted in astropy `table` version of catalogue. See [147](https://github.com/mattpitkin/psrqpy/pull/147).

- Update value, error formatting logic. See [145](https://github.com/mattpitkin/psrqpy/pull/145).

- Switch to a purely pyproject.toml-based build. See [144](https://github.com/mattpitkin/psrqpy/pull/144).
- Fix ATNF catalogue base URL to point to more up-to-date location. See [143](https://github.com/mattpitkin/psrqpy/pull/143). **IMPORTANT**: older versions of psrqpy will most likely no longer work.

- Ignore lines starting with `WARNING` in pulsar catalogue database file. See [139](https://github.com/mattpitkin/psrqpy/pull/139).

- Update the Galactic MSP table URL. See [135](https://github.com/mattpitkin/psrqpy/issues/135).

- Fix extracting the ATNF catalogue version number from the database file for v2.0.0 of the catalogue. See [132](https://github.com/mattpitkin/psrqpy/pull/132).