added timing support to jUnit XML reporter

Implemented support for report test timings in the jUnit XML reporter.

The implementation uses the new C++11 chrono functionality, but all
this has been encapsulated in only 3 lines at the top of the
JunitReporter class, which should allow for an easy adjustment for
non-C++11-compilers...
JunitReporter reimplemented using the new IStreamingReporter interface

* created new AccumulatingReporterBase class for accumulating test
results hierarchically and store them for a single processResults() call
after all tests have been executed; sections are currently not handled,
since their usage are optional and/or could be nested arbitrarily, which
would result in overly complex code, IMHO
* JunitReporter reimplemented on top of this new
AccumulatingReporterBase class
* added support for tracking time spend in each test case, each test
group, and overall tests to the base "*Stats" classes; this enables each
reporter (derived from IStreamingReporter interface) to report the
timings; for now only the JunitReporter takes advantage of that.
added a VS2012 project under the "projects" folder
added timing output to the console logger
added new timing related command line options

2 new timing related command line options have been added:
- performance-timings [-p]: print out performance timings per test case
and group
- performance-timings-threshold [-q <secs>]: print out only the timings
exceeding this given threshold value
Merge pull request #1 from Kosta-Github/Integration

Add timing support to console and junit reporters