Fix typo in documentation

Don't use `_dupenv_s` on MinGW.

Ensure the Windows folder selection returns a filesystem path (Closes #63)

Build Visual Studio examples statically for easier testing on old systems

Link examples with uuid.lib and ucrt.lib when using MinGW

Minor code refactor for clarity

Silence some compiler warnings on Windows

Implement pfd::path::separator()

Adapt OS X save_file() when default_path is a file instead of a directory (Closes #65)

Reorganise the example program to make it clearer

Add pfd::path::home() to retrieve the home directory

Fix zenity behaviour when default path is a directory

Implement a wrapper for getenv()

Workaround for an AppleScript file extension related bug (Closes #72)

OS X message box bugfixes