Fix: cpm download logic

See merge request !6

Feat: allow for multiple find package overrides

See merge request !5

Feat: bump CPM version

See merge request !4

This also checks if we are using the newest version of CPM and downloads it if necessary.
This should help with updating.

Feat: add private members in dev mode to doxygen doc

See merge request !2

Fix: enable `CMAKE_EXPORT_COMPILE_COMMANDS`

Closes #1

See merge request !1

Some third-party libraries depend on further third-party libraries and sometimes even share them.
With this custom find package command it is possible to overwrite the thrid-parties attempts of finding these libraries in order to use a downloaded version form our source tree.

Adding the object files to the final library target did not transfer any
linking information.
As stated here: https://cmake.org/cmake/help/latest/manual/cmake-buildsystem.7.html#object-libraries
using `target_link_libraries` honors the usage requirements.