create warnings for missing libs

docs/source/conf.py

@@ -51,7 +51,7 @@ try:
         "mwbase/windowmanager.hpp", "mwbase/world.hpp"])
         }
 except ImportError:
-    pass
+    print("WARNING: Unable to import breathe, code documentation won't be generated.")
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -86,6 +86,7 @@ try:
                                  int(cmake_data[26][1][1].contents))
 except ImportError:
     release = "UNRELEASED"
+    print("WARNING: Unable to import parse_cmake, version will be set to: {0}.".format(release))
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.