We need better issue/pull request templates

*How better?* I don't know!

Currently this issue contains only what *I think* could be useful, this needs more discussion but there are plenty things we could improve in our templates.

New templates that could be added:
- [x] Issue template for enhancements
- [ ] Issue template for documentation (?)

Improvements to existing templates that we could use:
- [ ] Checklist in pull request template, for example:
- If code changes were made, they have been tested
- I've updated the documentation (if applies)
- If this PR fixes an issue, I referenced them in the PR's description
- My code follow the code style of this project (Black)
- etc.
- [ ] Mention that lack of issue (or other prior discussion) may result in rejection
- [ ] Maybe add more types to choose from in pull request template (assuming the checklist from previous point won't just completely replace it)