refactor

[cjdoris]

Refactoring the codebase, which has got a bit out of hand.

• move all internal code into new Internals submodule
• all exported/public symbols defined in src/API/API.jl
• ensure tests pass
• use a common Internals.Common module which exports common functionality instead of needing to import functions from all over the place have each internal submodule export its internal API so other submodules can just do using ..Foo to get everything it needs
• make internal submodules more granular - e.g. have submodules for PyList etc within Wrap
• make internal function names shorter/clearer
• maybe move testitems from test to src?

[hhaensel]

@cjdoris @MilesCranmer
Just saw a big refactoring PR. Does that mean that we would need to refactor this PR?

[cjdoris]

@cjdoris @MilesCranmer Just saw a big refactoring PR. Does that mean that we would need to refactor this PR?

You will yeah but don't bother yet - this PR is likely to change some more.

Sorry for the delay on reviewing your PR, my time is currently limited and focused on bugs, improving code quality and working towards v1, rather than new features, but I will get to it.