Add code to parse Windows filenames properly -- or at least functionally

I really like Croon, but found that it wasn't working for me under Windows.  I see a Windows path with a drive letter and colon (but Unix-style '/' path separators) in the route_location, and so the split doesn't work properly.   This should work properly under Unix/Linux/OSX, but I haven't tried it under Cygwin on Windows.
It isn't single-line elegant, but it works well enough to allow me to use my favorite Web API documenting engine on my least favorite OS.