Fix a couple of SimplePager bugs

* Exiting with q was broken by d703320e38397c1b3bf9cb3fc4389f9c741c448b.

* We were only removing color codes in the case where the input string
  ends with a newline, which means we were overestimating the length of
  strings that don't end with newlines. After fixing that, SimplePager
  can accurately page through the inspect output for _pry_.