Continuedfractions

* refactor: speed up the convergents functionality using the standard recurrrence formula
* feat: split the`ContinuedFraction.mediant` method into separate methods for left- and right-mediants
* fix: complete revision of all docstring typesetting, including fixing all math. typesetting and Sphinx domain refs
* update doctests, Sphinx docs and unittests

* addresses 42: fix docstring typesetting + Sphinx HTML output configuration

* Refactoring of initialisation logic in `ContinuedFraction.__init__` to use [structural pattern matching](https://docs.python.org/3/tutorial/controlflow.html#match-statements) + update docstrings, doctests and unit tests
* Minor tweaks to function docstrings in `lib`

* Add [citation file format (CFF)](https://citation-file-format.github.io/) file
* More docs tweaks and improvements

* Closes 37 - add cached properties to `ContinuedFraction` for even- and odd-order convergents + update of docstrings, doctests and tests
* Small fixes and improvements to the docs

* Closes 36 - tweak [`ContinuedFraction.convergent`](https://github.com/sr-murthy/continuedfractions/blob/main/src/continuedfractions/continuedfraction.py#L634) method to pass in the full sequence of elements to [`lib.convergent`](https://github.com/sr-murthy/continuedfractions/blob/main/src/continuedfractions/lib.py#L236)
* Uses [slots](https://docs.python.org/3/reference/datamodel.html#slots) in `ContinuedFraction` class def. - ATM only for the `_elements` attr.
* Closes 35 - adds cached properties to `ContinuedFraction` to get all convergents and all remainders at once
* Update tests + docstrings + doctests + Sphinx docs
* Minor refactoring in [`lib.fraction_from_elements`](https://github.com/sr-murthy/continuedfractions/blob/main/src/continuedfractions/lib.py#L181)