Fixed -l option

Print an error message when invalid loglevel value is provided
Exit with an error code
Uses portable end of line instead of \n in error message
Print error messages on stdandard error instead of standard output
Improved option -x support

Print an error message when the command doesn't exist
Exit with an error code instead of 0
Merge branch 'master' of https://github.com/swaeku/newsbeuter