Added flag for single or comma separated stdin input values (#737)

[ariasmn]

There are a couple of things which I don't know if are ok:

• Variable/function naming. Non-native speaker so maybe the spelling is wrong.
• You can input from the stdin and a file (using both the -l and -u flags) at the same time.
• Did not add any tests because I didn't fully understand how these works. I can do some if needed with some guidance.

[ariasmn]

@ehsandeep @Ice3man543 Just wanted to check the current status of the PR and ask if there is anything more I could do to help

[ariasmn]

Done! Just updated the PR.

Please let me know if everything is ok.