(issue54) Implement a privilege drop to execute the program after installation. This commit is extremly ugly as I accidentally worked in a working tree that was partially merged with default. To review the real change please check the commit that will merge this branch into default.

find_program(SPHINX_EXECUTABLE NAMES sphinx-build
    HINTS
    $ENV{SPHINX_DIR}
    PATH_SUFFIXES bin
    DOC "Sphinx documentation generator"
)

include(FindPackageHandleStandardArgs)

find_package_handle_standard_args(Sphinx DEFAULT_MSG
    SPHINX_EXECUTABLE
)

mark_as_advanced(SPHINX_EXECUTABLE)