Remove automagic versioning

[ctrueden]

The setuptools_scm project is very cool, but it has two showstopping issues:

1. It limits us in how we bump version numbers according to SemVer. At least: I can't figure out how to e.g. change the minor version digit, not the patch version digit.
2. It causes errors, at least on my system, with missing _version.py files when trying to make a release.

I'd rather just have concrete manually managed versioning.

[gselzer]

Alright, I did a little more research @ctrueden, and I'm in agreement that the simplest path of manually managed versioning is probably the way to go.

With that in mind, we want to specify the version in two places:

1. At build time. We used to do it in setup.py, but due to PEP 621 I think it's best done in pyproject.toml. With that in mind, we might as well wait until the merge of Migrated the metadata into PEP-621-compliant pyproject.toml. #46.
2. At runtime. There are two options. The simpler option would be to hardcode the version in src/scyjava/__init__.py, with a simple test that ensures that the hardcoded versions are the same. The more complicated option (although we already have coded the complexity) is retaining the case logic currently in src/scyjava/__init__.py.

Do you have a preference @ctrueden?