add uninstall target

[rgetz]

Per the request #694, this adds an "uninstall" target, which is (a) good form, and (b) requested by Jeff Long, and will make PyBOMBs work more natively.

[willcode]

Thanks!

[pcercuei]

The license of the code you referenced in the gist is uncertain...

The code would also need to respect the DESTDIR environment variable.

[willcode]

From SoapySDR (Boost Software License):
https://github.com/pothosware/SoapySDR/blob/master/cmake_uninstall.cmake.in

GNU Radio (GPLv3)
https://github.com/gnuradio/gnuradio/blob/main/cmake/cmake_uninstall.cmake.in

From the CMake wiki (presumable meant to be used under any license)
https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#can-i-do-make-uninstall-with-cmake

[rgetz]

I will refactor based on this one: which should be better:
https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#can-i-do-make-uninstall-with-cmake

the license for that is explicit -

CMake is distributed under the OSI-approved BSD 3-clause License.
See the licensing page for details.
The snippets on this wiki are provided under the same license.

[rgetz]

updated