Add support for the "OnlyShowIn" and "NotShowIn" tags
Merge the modified origin repo with the OnlyShowIn/NotShowIn commit and fix two issues:

- name of the command line option
- the use of $XDG_CURRENT_DESKTOP is now an opt-in
Merge pull request #29 from flyingDavid/environment

Add support for the "OnlyShowIn" and "NotShowIn" tags and merge with upstream commits