Transdoc

🔧 FIXED 🔧
* Installing `transdoc[python]` now works since I have worked around the bootstrapping problem by doing two releases.

✨ NEW ✨
* Transdoc now uses the Python packaging entrypoints system to detect and register plugins
* Plugins allow Transdoc to support transforming documentation in many more languages
* The library has documentation available at [maddyguthridge.github.io/transdoc](https://maddyguthridge.github.io/transdoc)
* The `--help` message now has pride in it!

💣 BREAKING CHANGES 💣
* The library no-longer supports Python docstring transformation out-of-the-box.
* Instead, you need to `pip install transdoc[python]` to install the dependencies required to modify Python docstrings.
* This will be added in the `v1.0.1` release to avoid a bootstrapping problem.

✏️ CHANGED ✏️
* Basically everything. It's essentially a brand new library.
* Error messages are much more reliable, even if they are much more verbose (I'll work on that if I have the energy).

Display full error message when an exception is raised while importing a rules file

* I have a 🏳️‍⚧️ new name 🏳️‍⚧️
* Updated the project URLs and copyright etc to reflect this

* Fix an issue where multi-line transformations weren't correctly indented

🔧 FIXED 🔧
* Type safety issue with `mypy` due to function and module naming conflict
* When transforming into an existing directory, existing files weren't removed