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.

[mwip]

I tried to wrap my head around this. @jgrn307 what do you think would be the best place to implement this? I think it would be best to put some path.expand() in gdal_cmd_builder() but I am not quite sure if that is to your liking?

Another option would be to parse [src|dst]_[datasource|filepath|filename] through path.expand(). This could be favored, gdal has so many names for these files. Sometimes with flags, sometimes without... Gosh I love long grown software projects 🤣

If you let me know I will work on a PR.