Add support for devtools / rspec2

Opening early to have a track record

* Adds devtools
* Switches to rspec2
* Renames spec files around to handle mutant conventions
* Not all mutations are killed (mutant coverage is IMHO many times harder than heckle)
* Metrics scores are higher, this is a result from doing development under 1.9.3 (MRI). No negative changes only measurement diffrencies from flay/flog.
* Removes jeweler and provides gemspec like the other dm-2 style gems

This branch runs ```rake ci``` (devtools is prepared to handle metric differences). So lets wait till the build is green to have no "suboptimal quality" merge.