v0.6.0

This is the beginning of a new stable branch. I reviewed all the diffs between the v0.4 branch and master and I merged all the fixes from both into 0.6.0.

I moved the "futures timeout and cancellation API" experiment to a separate branch. So all the experimental features (*) are now in feature branches and the master is aligned on 0.6.0 (except for the version number which is bumped to 0.7.0 in the master). There is no guarantee that any of these experiments will ever get published in a stable version.

(*) except for the --generators option that I am now including by default because it passes all unit tests and seems pretty solid.

This version fixes some recently reported issues:

#149 streamline-express broken with fibers; works with callbacks (Brian Downing)
#148 _getEncoding() should be less aggressive in returning utf8 (Anurag Biyani)
#147 Support harmony generators
#146 Different behavior with and without fibers, at least in mocha (Brian Downing)

I have also done some cleanup and debugging on the stacktrace feature. In callbacks and generators modes, the stack string now contains both the reconstructed stack and the raw stack and they are clearly delimited. In fibers mode, I fixed a bug which caused incomplete stacktrace when execeptions were thrown from futures. The "stack-test" unit tests now pass in the 3 modes.