docs: use a single bibtex cite instance for lists (#35)

* refactor: use `import_dependency` to import optional packages
* docs: update badges on `README.rst`
* docs: add citation file
* chore: update `MANIFEST.in`
* chore: bump version to `1.1.2`

feat: output average Earth's density in ref_ellipsoid (#25)

feat: add changes to post to pypi (#17)

feat: add function for attempting to extract projection (#11)