Create tests for each stdisplay tool

[ben-grande]

They aim to emulate common utilities, so check if their behavior is the same.

Each tool must have a test for its ability to behave the same as its counterpart:

1. If a file descriptor is read from to written to
2. If it takes file arguments, how many does it accepts
3. What happens when it receives no argument
4. Behavior when it can't write to a file, does it still write to stdout
5. Buffer types, does it start writing before reading everything
6. It it reads from stdin, does it requires - or reads automatically from it or both

Each test must also have a small test with ANSI escape sequences to check if stdisplay is being used.

[ArrayBolt3]

@adrelanos Can this be closed? All of the stdisplay tools have tests now that #25 has been merged.