base::copy_file implementation

[doomed-phobos]

Hi!

This change, in short, implements base::copy_file function based on the idea of copying and pasting memory blocks. I've also changed the functions (move, copy and delete file) that throw exceptions unnecessarily to return bool type. (It needs clarify that I'm not an expert :sweat_smile:)

[dacap]

Thanks for your contributino @doomed-phobos, at the moment we'd prefer to keep the original behavior of the functions (throwing exceptions).

I'll add some comments to your copy_file implementation just in case if you want to complete it.

[dacap]

Implemented with https://github.com/aseprite/laf/commit/f5ed6fc4dc629e152ff3de42acedfc1c5e601c4b