* First compiling pass, doesn't link tests, looks like templates aren't properly initialized?

* Make reduce inline, compiles, sum passes test

* Initial working reduce op builder

* Add Std dev, Variance, L2Norm. Tests fail because Power isn't actually implemented in ngraph++ yet

* Add Doc Strings, slight refactor

* fix tests after master merge

* Fix style issues raised in PR review

* Switch to Sum-based ops instead of Reduce-based ops for simpler autodiff.

* Add requested TODO comments

* Use all_close for tests

* Remove product op