Add a extract option to obtain shapes from RDF data

[labra]

Add a extract option to the command line so rudof can be used to extract a shapes (ShEx or SHACL) from RDF data or endpoints. This functionality is already supported by another project in WESO called sheXer and we could approach it in two ways:

• Implementing a new extractor in Rust using our experience with sheXer which could probably be more performant than the python one.
• Leveraging on the existing sheXer extractor and create a wrapper on top of it invoking Python code from Rust. This alternative seems easy at first, because we can just leverage sheXer.

@DaniFdezAlvarez indicated that he was planning to refactor sheXer's code but he may continue with Python or try to rewrite it in Rust.