Layer unit tests #29

Tested/passed:

• activations.h
• activations.cpp
• conv1d.h
• conv1d.cpp
• dense.h
• dense.cpp
• maxpool1d.h
• maxpool1d.cpp
• conv2d.h
• conv2d.cpp
• maxpool2d.h
• maxpool2d.cpp

Need to test (before March 1st)

• integration testing full nn4mc flow
• finishing up all padding options