Add ability to use TopQuadrant SHACL implementation as engine

[gtfierro]

• two new functions: utils.shacl_validate and utils.shacl_infer which try to use TopQuadrant if available and default to pySHACL otherwise. User can opt-in to either engine
• new install extra "topquadrant", which enables the TopQuadrant SHACL engine
• updating tests and deps to deal with the added engine

[gtfierro]

@MatthewSteen @TShapinsky where do you think I should document the two different SHACL engines? Under "explanations" in the docs?

[TShapinsky]

@gtfierro What is the reason to drop support for python 3.8? It's still fairly modern (2019) and is the default python for ubuntu 20.04 which is still used by a lot of people. I'd prefer not to drop support unless we have to.

[gtfierro]

@gtfierro What is the reason to drop support for python 3.8? It's still fairly modern (2019) and is the default python for ubuntu 20.04 which is still used by a lot of people. I'd prefer not to drop support unless we have to.

I thought that our dependencies (rdflib 7, for example) had dropped 3.8 but they only dropped 3.8.0! I've changed this so it's compatible with 3.8.1 or higher

[TShapinsky]

@gtfierro What is the reason to drop support for python 3.8? It's still fairly modern (2019) and is the default python for ubuntu 20.04 which is still used by a lot of people. I'd prefer not to drop support unless we have to.

I thought that our dependencies (rdflib 7, for example) had dropped 3.8 but they only dropped 3.8.0! I've changed this so it's compatible with 3.8.1 or higher

Cool! That seems good to me, I doubt anyone is using 3.8.0

[gtfierro]

@TShapinsky this should be ready for review now!

[gtfierro]

@TShapinsky can you approve when you get a chance? thanks!

[MatthewSteen]

@MatthewSteen @TShapinsky where do you think I should document the two different SHACL engines? Under "explanations" in the docs?

Probably explanation (understanding-oriented) or reference (information-oriented), which might be a better fit.