to_posix_string and to_windows_string functions

[hcarty]

Along the lines of #1 it would be useful to support POSIX and Windows path renderings for applications which may communicate across platforms.

[rseymour]

I could use this as well. Either as to_posix_string / to_windows_string or a way to treat a path implicitly as the compiled platform (default) or a chosen platform in most functions. For instance reading in "C:\whatever\thing.exe" on a mac should be able to be flagged and treated as "C://whatever//thing.exe" and get the same filename/basename considerations as it would on windows.