Build regular expression

[rodedzats]

We need to extract stack traces from stackoverflow questions. In order to recognize the stack-traces we need a regular expression string that matches all possible stack traces in that question.

[rodedzats]

Created a class for extracting stack traces, tested it on the following page (question and best answer): http://stackoverflow.com/questions/3988788/what-is-a-stack-trace-and-how-can-i-use-it-to-debug-my-application-errors The implementation is based on the initial work of @yosefraisman