properly escape windows paths

Windows uses `\` as its path separator by default, so anything passed through the native node.js `path` methods spits out an unexpectedly backslashy string. Luckily we can get around this problem by being as slash-nostic as possible. There were two basic steps in the final solution:

- Escape backslashes before passing strings to the `RegExp` constructor
- Convert file paths returned by `glob` into the appropriate OS-specific path (read: convert `/` to `path.sep`)