Added pauseTyping() and continueTyping() Methods.

I think the commented out stop() function was having issues because there is a jQuery function called stop() and when dealing with a jQuery object and trying to chain the methods the names were clashing.

I ended up renaming the method pauseTyping() as i think this is a better explanation of what i've implemented. I needed two methods to pause and continue typing. So if the typerwriter was actually backspacing i wanted the continue typing method to carry on where it left off backspacing.

This meant i needed to add an extra variable on self called 'backspacing' and set that boolean in the typewrite() and backspace() methods.

Check out this codepen to see it in action - http://codepen.io/ralcus/pen/pvjObB/

You may want to go a different route with your stop and start methods. But either way i hope this pull request is of use/help.