added new episode number option for increase and decrease commands

[mparadinha]

Just added a new option on the argument parser to allow a number to be given after the anime-regex. Because I choose the default as 1 I didn't really need to change a lot in the rest of the code. I can't test it because of the current 403 error that occurs. This takes care of issue #16

[alexkubica]

Looks good to me.

[ryukinix]

Looks fine

[ryukinix]

Thanks!