Turn xdg-user-dir-lookup into xdg-user-dir

We build a C program that does the same of our shell script, just in a
worse and buggy way.
Install the C program instead of the script.

[endlessm/eos-shell#4048]
Update .gitignore

[endlessm/eos-shell#4048]
Merge pull request #3 from endlessm/shell/4048

Shell/4048