Windows paths

[DanieleDiBenedetto]

• Add support to be able to parse Windows paths;

[DanieleDiBenedetto]

For C++ FFI it seems that it's necessary to separate the way on how paths are parsed depending if you are on Windows or *nix operating systems. The reason is that the OsStr implementation:

• On POSIX systems, boils down to &[u8], because POSIX functions accept and return byte strings;
• On Windows, OsStr can be thought of as an &[u16], because Win32 Unicode functions accept and return strings as arrays of 16-bit units.

The usage of CStr to parse the path doesn't solve the problem because it assumes an UTF-8 encoding.

This may seem a weird edge case, in which a Windows string is not UTF-8 encodable, but can happen quite easily for any user with a non latin alphabet.

The approach to be followed in this situation should be similar to ZCash's one