CMakePPCore -> CMakePPLang Rename

[zachcran]

Description

This PR partially accomplishes #28 by renaming this repo (to the extent that I can) to CMakePPLang, as per my discussion with @ryanmrichard on January 25, 2022.

So far, I have performed a case-insensitive, project-wide find and replace for:

• CMakePPCore -> CMakePPLang
• CMakePP Core -> CMakePPLang
• CMake PP Core (didn't exist)
• cmakepp_core -> cmakepp_lang
• CMAKEPP_CORE -> CMAKEPP_LANG
• cmakepp-core (didn't exist)

TODO

• [ ] Make sure the renaming did not break tests.
• [x] Prepare a PR in CMaize with name changes.
• [ ] Once this PR is accepted, the repository will need to be renamed as well.

[zachcran]

@ryanmrichard Although the checks are failing, I believe this is ready to go (see paragraph below). After this PR is merged, this repository needs to be renamed to "CMakePPLang" and then CMaize PR #63 can be merged as well. Once the renaming and CMaize PR are done, the failing CI tests should be rerun to make sure that everything succeeds after the renaming.

To get the unit test for class.cmake to succeed on my Linux machine, I had to set -DFETCHCONTENT_SOURCE_DIR_CPP to a local version of CMaize with the "CMakePPCore" to "CMakePPLang" changes already implemented. My local unit test error was the same error you see in the CI output (link) about /path/to/CMakePPCore/CMakePPCore/build/tests/tests/class.cmake/src being a directory when a file is expected. There appears to be references to CMaize used in the unit testing of CMakePPLang, which, I think, is causing this weird cyclical issue. See L4-12 of CMakePPCore/tests/CMakeLists.txt (link) for the first place I found CMaize included.