Adjust frames to display ErrorException

I added a new method `getFrameFromError` to correctly display details regarding the generated ErrorException. This is related to #47.

Sometimes when generating frames for ErrorException the reported line is the line ahead i.e. a syntax error has occurred. Subtracting (-1) does not work since the previous line will be reported for other cases i.e. accessing a private property. I believe that this acceptable since this how PHP reports errors anyway. The only downside (?) is that the next line is highlighted in codeblock (have a look at https://github.com/filp/whoops/issues/47#issuecomment-19101909).