Add release checklist and PR template

Author: rhpvorderman

.github/PULL_REQUEST_TEMPLATE.md

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+
+### Checklist
+- [ ] Pull request details were added to CHANHELOG.rst

.github/release_checklist.md

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+Release checklist
+- [ ] Check outstanding issues on JIRA and Github.
+- [ ] Check [latest documentation](https://python-isal.readthedocs.io/en/latest/) looks fine.
+- [ ] Create a release branch.
+  - [ ] Set version to a stable number.
+  - [ ] Change current development version in `CHANGELOG.rst` to stable version.
+- [ ] Merge the release branch into `main`.
+- [ ] Create a test pypi package from the main branch. ([Instructions.](
+https://packaging.python.org/tutorials/packaging-projects/#generating-distribution-archives
+))
+- [ ] Install the packages from the test pypi repository to see if they work.
+- [ ] Created an annotated tag with the stable version number. Include changes 
+from CHANGELOG.rst.
+- [ ] Push tag to remote.
+- [ ] Push tested packages to pypi.
+- [ ] merge `main` branch back into `develop`.
+- [ ] Add updated version number to develop.
+- [ ] Build the new tag on readthedocs. Only build the last patch version of
+each minor version. So `1.1.1` and `1.2.0` but not `1.1.0`, `1.1.1` and `1.2.0`.
+- [ ] Create a new release on github.
+- [ ] Update the package on conda-forge.