Auto-expand home directory alias in file paths

[mwip]

Using the alias '~/some/file.tif' for the paths relative to the home directory does not work. Using the full-path (i.e. '/home/user/some/file.tif') instead works just fine. I experienced that with gdal_translate on Ubuntu 18.04 LTS (R 3.6.3).

A solution would be to parse all parameters with file paths through path.expand() on Unix-like systems. To my knowledge, that would not interfere with Windows systems.