Added a 'backSpeed' option

Added a 'backSpeed' option and default so it's possible to have different backspacing and typing speeds.
Added the ability to pause mid-sentence

Added a timeout  option mid sentence if an escape character is used before a pause value. The escape character used is '^'. For example..

strings: ["This is my sentence with a pause^1000 in the middle"]

The code does the following:
- Checks for the escape character '^'
- Checks for the next whitespace in the sentence, and takes the value between '^' and ' ' as a value
- Removes the escape character and pause value from the string so they're not printed
- Pauses on the next loop for the duration of that value
Merge pull request #18 from crdunst/master

Added a 'backSpeed' option & escape character to pause typing