Tidy up streographic code + StructureLibrary changes

[pc494]

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name: Tidy up streographic code + StructureLibrary changes
about: This deletes some old code and streamlines the StructureLibrary class

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Release Notes

major (and breaking)
improvement
Summary: 1 line per end-user relevant change

What does this PR do? Please describe and/or link to an open issue.

1. Deletes the old streographic library function (superceded by Rotation lists from streographic gridding #55)
2. Removes the StructureLibraryGenerator and replaces with classmethods.

Describe alternatives you've considered
Discussion on (2)
Previously our syntax involved using a generator that didn't do any "science" to create a library. I feel (@dnjohnstone please weigh in) that

from diffisms.libraries.structure_library import StructureLibrary
StructureLibrary.from_orientation_lists() 
StructureLibrary.from_crystal_systems()

Is a clear syntax, both for end user and developers. To claim what these methods do is "generation" seems a bit rich as it's just combining things with loops. c.f with DiffractionGenerator

Work in progress?
If you know there is more to do, make a checklist here:

• Catch missing coverage
• Docstrings
• Get "philosophical approval"

[pc494]

@dnjohnstone can I get conceptual approval on this so that I can go tidy up docstrings etc to get it ready to merge?

[dnjohnstone]

@dnjohnstone can I get conceptual approval on this so that I can go tidy up docstrings etc to get it ready to merge?

Thanks @pc494 - yeah I agree that this is an improvement. I think we got a bit Generator happy at that point.

As an aside, also noticed that we should be documenting Generator classes differently https://docs.scipy.org/doc/numpy-1.15.0/docs/howto_document.html#documenting-generators i.e. have "Yields" rather than "Returns"

[pc494]

Cool, I'll tidy that up today then.

I'm not so sure about the second part though, I think they mean generators in the formal sense (with yield statements and all) whereas our "Generators" are really just normal classes.

[dnjohnstone]

Cool, I'll tidy that up today then.

I'm not so sure about the second part though, I think they mean generators in the formal sense (with yield statements and all) whereas our "Generators" are really just normal classes.

Good point, thanks - fuzzy brain.