STDIN input added

[SergeyBurtsev]

May I suggest that rstfilter could use STDIN input as an option?

[ko1]

or use STDIN if a script file is not given?

[SergeyBurtsev]

First of all, thank you very much for your open-source work, @ko1 ! Using STDIN if no script is given is better idea, thank you! I will reopen PR with new change.