Complete remaining cat functionality

[tacoda]

Complete the remaining use-cases of cat as defined by GNU Coreutils here.

These include:

1. When called with no arguments copies STDIN to STDOUT
2. When called with multiple files it outputs all content
3. Add options, which are mostly about showing/hiding nonprinting characters
4. When called with multiple files and - it outputs all contents including STDIN

[tacoda]

@faraazahmad I'm planning on implementing as much of Coreutils functionality as possible. I chose to start with cat. I will be getting started on this soon. Any feedback you may have is welcome!