Continuous improvement of export_cpp

This MR includes the following improvements:

• Fixed issue with number of elements in activation (fix #41 (closed));
• Added support for memory wrapping in activation;
• More static concat, works with any type;
• Restored LeakyReLU export;
• Make Quantizer use activation templates;
• Fixed saturation value in activation_forward_value();
• Fixed wrong convolution implementation with dilation (fix #40 (closed)).