Split monolithic LayerParameter into per-layer Protobuf Messages

[shelhamer]

Split LayerParameter into PoolingLayerParameter, ConvolutionLayerParameter, and so on for layer-specific params. This will be self-documenting in terms of what params each layer accepts.

There should perhaps be a "base" LayerParameter with common fields.

Layers and LayerConnections should could go away. There's no need for the

layers {
   layer {
     ..
   }
 }

incantation.

For backwards-compatibility, the current caffe.proto will be frozen as caffe0.proto. A translation script from caffe0.proto to the new caffe.proto should be implemented to help migrate models.

Don't fret, this is only a one-time break to fix the schema for the 1.0 release.

[sguada]

@jeffdonahue @shelhamer I'm working in refactoring DataLayer into DataSource and DataPreprocessing, and changing caffe.proto. If you work on this let me know so we can coordinate.

[jeffdonahue]

I'm working on this, will probably have some commits pushed tonight or tomorrow.

[shelhamer]

Closing, since this is accomplished by #219.