build_sphinx.py needs cleanup

[butler]

The build module should properly cleanout everything before rebuilding. Also if a destination directory does not exist it should be created. Currently there are several instances of checking for existence but failing to create if not true — the script just goes on happily to next if statement leaving no message of why the end product cannot build properly. Finally it should exclude irrelevant files from the document scrapping (such as setup.exe and setup.mac). There may be other things as well.