Single Cmake build/test system for APBS/PDB2PQR with Travis CI integration about apbs

[sobolevnrm]

@intendo has made a lot of progress on this. I still need to move Scons tests over.

@intendo can you update the documentation (somewhere) with these build instructions you sent?

rm -rf build && mkdir build && cd build && cmake -DENABLE_PYTHON=ON .. && cmake --build . && ctest . && cd ..

[intendo]

The CMake/test system for APBS is mostly complete for Linux and MacOSX using Github Actions rather than Travis CI.

The build instructions for APBS has been put in a script in the apbs directory called .build.sh that is useful for developers to do end to end build with CMake, test with CTest, and package with CPack.

[intendo]

The has been implemented and documented.
It works for Mac and Linux with Github Actions and on Windows with Appveyor.
The build is done with CMake, tests are done with CTest, and packaging is done with CPack.