Added better docs; added PRNGKeys. Packaging with pyproject.toml.

Also added support for matching dtypes using regexes, and for nesting e.g. Shaped[Float[Array, "dim1 dim2"], "dim3"].

docs/.citation.md

@@ -0,0 +1,12 @@
+If you found this library to be useful in academic work, then please cite: ([arXiv link](https://arxiv.org/abs/2111.00254))
+
+```bibtex
+@article{kidger2021equinox,
+    author={Patrick Kidger and Cristian Garcia},
+    title={{E}quinox: neural networks in {JAX} via callable {P}y{T}rees and filtered transformations},
+    year={2021},
+    journal={Differentiable Programming workshop at Neural Information Processing Systems 2021}
+}
+```
+
+(Also consider starring the project [on GitHub](https://github.com/patrick-kidger/equinox).)