allow --relocatable to work on Windows
remove "Also this does not currently work on Windows" from doc
move init of `interpreter_ext` init inside if/else as requeted by @piotr-dobrogost
use `path_locations()` to deal with os differences in paths, refactor `shebang`/`new_shebang` init
Merge pull request #401 from jpenney/feature/windows_relocate_issue49

allow --relocatable to work on Windows