Changelog:
- Guard __has_attribute for compilers that don't support it.
- Fix memory access bug in PyImath::FixedVArray<T>::getitem.
- Allow control of install destination for python modules, via PYIMATH_OVERRIDE_PYTHON_INSTALL_DIR.
- CMake targets to build documentation.
Signed-off-by: Martin Reboredo <yakoyoku@gmail.com>