Use find_package to locate Sphinx

Author: aobolensk

cmake/sphinx.cmake

@@ -1,6 +1,7 @@
 option(USE_DOCS OFF)
 if(USE_DOCS)
-  set(SPHINXBUILD "sphinx-build")
-  set(SPHINXINTL "sphinx-intl")
+  find_package(Sphinx REQUIRED)
+  set(SPHINXBUILD "${SPHINX_EXECUTABLE}")
+  find_program(SPHINXINTL sphinx-intl)
   set(SPHINXOPTS "-W" "--keep-going" "-n")
-endif(USE_DOCS)
+endif()