[example] convert mnist name fix (crashes xcode compiler)
Merge pull request #1033 from qipeng/dev

[example] convert mnist name fix (crashes xcode compiler)
[docs] default setting for layout
Merge pull request #1034 from sergeyk/dev

[docs] default setting for layout
add SILENCE layer -- takes one or more inputs and produces no output

This is useful for suppressing undesired outputs.
Merge pull request #624 from jeffdonahue/squash-layer

SILENCE layer -- takes 1 or more inputs and produces no output (kudos to @longjon for fixup)
shift CUDA code out of common
groom proto: sort layer type parameters, put loss_weight after basics
add engine parameter for multiple computational strategies

add `engine` switch to layers for selecting a computational backend when
there is a choice. Currently the standard Caffe implementation is the
only backend.
ifdef engine default
strategize Caffe convolution
strategize pooling

Scaffold engine switching for pooling.

The Caffe pooling is instantiated without regard for engine in:
- LRNLayer
- PoolingLayer tests
- StochasticPoolingLayer tests
- MaxPoolingDropout tests
strategize relu, sigmoid, tanh
strategize softmax
grooming: drop pointless overrides, stub layer comments
default engine to Caffe according to compile flag
default engine to Caffe in case config is missing