added Python script Tests/PerformanceTests/test_performance.py with same functionality as App/TestPerformance

purged a couple of unnecessary boost/shared_ptr includes (we are now using std::shared_ptr throughout)

SWIG bindings now incorporate Doxygen comments (can be done automatically during build process via BORNAGAIN_GENERATE_PYTHON_DOCS switch)

Functions mag, mag2, magxy, mag2xy always return double (and no longer complex for complex vectors). This closes Bug #1358. BROKEN (customformfactor.py fails; see Bug #1359).

cmake now generates bindings during build automatically. can be disabled by setting BORNAGAIN_GENERATE_BINDINGS to FALSE

Minor updated to Python binding generation. CMake will now default to Python 2.7, unless the preprocessor directive BORNAGAIN_USE_PYTHON3 is defined to be TRUE. I have only tested building against Python 3 on Linux -- on Windows and MaxOS the build process will likely fail, without additional modification to CMake scripts.