non-OS-indepdent path separators

[baconpaul]

No description provided.

[djtuBIG-MaliceX]

Have to use std::replace(). As with #59 I opted to use that in combination with fs::absolute() as a form of normalisation. Might be worth generalising when passing paths between string_to_path() and path_to_string() as a global sanitisation operation. Overhead introduced does not affect real-time performance and is likely to only take place during bank/sample load operations.

[rudeog]

Back when I was fluffing up the configuration.cpp I did some work on some path functions (see functions ending in _path). It might be a good idea to have some of this functionality in utilities, and we could add functionality for slash conversion.

[baconpaul]

I'm going to close this since I think the solution is to use fs::path operator/ everywhere