Support regular expressions/multiple files

I implemented support for regular expressions or multiple files. Basically it's the same, since regular expressions are expanded to multiple files by the shell. Although, i did not get this to work with files that contain a space character in it. For some reason, `lpr` and `scp` even acted completely different (and weird) when I tried to set `"`s around the filenames. 

`lpr` completely ignored the `"` and scp used the `"` as it's filename. I was able to work around the `scp` problem by using `bash -c string_as_command`, but this did not work for `lpr`. Probably there is an easy solution for this, but I'm a bash noob so... :D 

Also, files with paths are still not supported. And I updated the README.md.