Package cleanup

[gselzer]

Goals of this PR:

• Refactor imglyb/ directory into src/imglyb/ directory. See this article for the benefits
• Minimize setup.py in favor of setup.cfg. This seems to be the preferred approach nowadays.
• Add a linting strategy (using black)
• Add a code coverage strategy
• Allow these features to block merge through Github Actions

Closes #15

[codecov-commenter]

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[gselzer]

One thing I think would be slick is exporting these actions to a separate repo. There is a lot of overlap with scyjava, pyimagej.

We may be able to follow the outline presented in number 2 here

[ctrueden]

Woot!