Add [SPDX][1] licensing/copyright tags to the `get_cpm.cmake` script,
so that anybody that copies the `get_cpm.cmake` script into their repo
(following the instructions in the README.md)
will automatically comply with CPM's MIT license.
[1]: https://spdx.dev/
* get_cpm: Recover from failed download
If the download fails during the cmake config step
an empty `CPM_<version>.cmake` file is created.
So far the script only checks the files existence,
so there is no second try until the empty file is deleted manually.
This adds a check if the file is empty
and resumes the download on next config if it is.
* More descriptive function name
* Expand absolute path later in get_cpm.cmake
Supports expanding tildes in the environment.
* Apply cmake-format to get_cpm.cmake
* Use .cmake-format file
* apply clang-format and cmake-format and add style check workflow
* add declare package definition
* add additional public methods and rename internals
* change development verison tag to 1.0.0
* rename internal method
* rename public method
* rename test var
* update copyright and fix comment
* typo
* run fix-format
* fix test function names
