Pyripherals

Summary Changes
- Update JOSS paper according to reviewer feedback
- Update documentation
- Replace `twos_comp` with `int_to_custom_signed` and `custom_signed_to_int`
- Allow appending to files with `DDR3.save_data`
- Add Python test workflow on commits and PRs to main

What's Changed
* Faster twos_comp by Ajstros in https://github.com/Ajstros/pyripherals/pull/16
* Updated i2c pipe data transfer by cnbecks in https://github.com/Ajstros/pyripherals/pull/17
* Ads sync by lucask07 in https://github.com/Ajstros/pyripherals/pull/19
* Bitfile versioning by Ajstros in https://github.com/Ajstros/pyripherals/pull/18
* Fix bug where end of last save gets cut off and not all data is returned by Ajstros in https://github.com/Ajstros/pyripherals/pull/20
* Fix paper line length by Ajstros in https://github.com/Ajstros/pyripherals/pull/21
* Fix Python App Workflow by Ajstros in https://github.com/Ajstros/pyripherals/pull/25
* Joss Revisions by Ajstros in https://github.com/Ajstros/pyripherals/pull/27

New Contributors
* cnbecks made their first contribution in https://github.com/Ajstros/pyripherals/pull/17

**Full Changelog**: https://github.com/Ajstros/pyripherals/compare/v0.0.2...v0.0.3

- Add `addr_step` option for `Endpoints`
- Fix bug where `WriteRegister` calls were using `Endpoint` bit indices instead of addresses
- Add `DDR3` setup functions
- Add `ads_seq_cnt` to data read from DDR
- Change `to_voltage` and `from_voltage` to use `np.arrays` (much faster than old list comprehensions method)
- Fix `impedance_analyzer.py` example