Add Python bindings

[labra]

One goal of shex-rs is that the library can be invoked from Python. Pyo3 seems to be the library that can help to create these bindings.

A sister project that does this is oxigraph, and here is their source code that we could look for inspiration.

[labra]

First version with Python bindings has been published as 0.0.14.

@angelip2303 Can we close this issue and open later more specific issues about other features that may be required?