Read token as input for mfa script and added new assume_role script

[albac]

Awesome tool! Simple and easy to use than other tools I found on the internet.

I have been using it for a while so I decided to add some of my own improvements.

I wasn't sure about adding assume_role script here, I can create another repository for only assume_role if you want, but I wanted to post it here and get your feedback first.

[asagage]

Thanks for your contribution. Please resolve conflicts and I will merge.