Bugfix/docs installation (#1438)
Bugfix/docs installation (#1438)

* 'Existing Install Hints' fix

Errors in some CMake variable names resulting in:
- being ignored: 'DExpat_...' instead of 'Dexpat_...'
- error: 'pybind11_ROOT' instead of 'Dpybind11_ROOT'

Signed-off-by: Derek Severin <4cdcd77726442601ca9ffde734644eaeddcd23f5@gmail.com>

* 'PYTHON_PATH' instead of 'PYTHONPATH'

Use of wrong variable 'PYTHONPATH' instead of 'PYTHON_PATH'.
'PYTHONPATH' might not be defined and can contain more than a single path, resulting in invalid values for the 3 variables 'DPython_LIBRARY', 'DPython_INCLUDE_DIR', 'DPython_EXECUTABLE' provided to cmake.

Signed-off-by: Derek Severin <4cdcd77726442601ca9ffde734644eaeddcd23f5@gmail.com>
AcademySoftwareFoundation/OpenColorIO,AcademySoftwareFoundation/OpenColorIO,AcademySoftwareFoundation/OpenColorIO,AcademySoftwareFoundation/OpenColorIO,AcademySoftwareFoundation/OpenColorIO