* declare sigmoid for core fusion

* add simple test for sigmoid

* info fusion status

* cp op as main op

* builds as expected

* move sigmoid fusion code

* add reference kernel

* sigmoid bprop reference kernel and clang-format

* add delta to bprop

* fprop called

* compiles bprop

* move tests

* serializer support

* address comments in code

* add doc

* naming similar to core ops

* fix failing test

* fix failing test

* address clang issue

* more changes

* change test macro