New Examples, Bug Fixes, and Layers

New examples:

• Learns Hypotenuse
• Simple Image Classifier with Parallel Convolutions
• Simple Plant Leaf Disease Classifier

Fixes bugs #31 and #32.

Adds new layer types:

• TNNetReLUSqrt: does a ReLU followed by square root.
• TNNetPower: calculates the power function.

Documentation updates.