Refactoring for Python conventions

[truth-quark]

These will be split over a few PRs:

• Fix naming and namespaces
• Move code & tests to sub-directories
• Compress KEM and Sig classes into single class each with data & methods. Match obj interface to the OQS C interfaces for KEMs and Sigs.
• Context manager for KEM & Sigs
• Clean up module level variables? (& context manager for opening the SO?)

[truth-quark]

Several of the fixes are covered in https://github.com/open-quantum-safe/liboqs-python/pull/6

[dstebila]

6 is now merged, anything else left in this issue?

[vsoftco]

https://github.com/open-quantum-safe/liboqs-python/commit/92daf9681e56e9eed1ff81e2a01ebb46c1c582e2 closes this issue