Add more useful string description of layers.

Adds:
 - pbb in Dropout and SpatialDropout
 - non default params in SpatialConvolution, SpatialConvonlutionMM, SpatialMaxPooling

Dropout.lua

@@ -40,3 +40,7 @@ end
 function Dropout:setp(p)
    self.p = p
 end
+
+function Dropout:__tostring__()
+  return string.format('%s(%f)', torch.type(self), self.p)
+end

SpatialConvolution.lua

@@ -119,3 +119,15 @@ function SpatialConvolution:type(type)
    self.fgradInput = torch.Tensor()
    return parent.type(self,type)
 end
+
+function SpatialConvolution:__tostring__()
+   local s = string.format('%s(in: %d, out: %d, kW: %d, kH: %d', torch.type(self),
+         self.nInputPlane, self.nOutputPlane, self.kW, self.kH)
+   if self.dW ~= 1 or self.dH ~= 1 then
+      s = s .. string.format(', dW: %d, dH: %d', self.dW, self.dH)
+   end
+   if self.padding ~= 0 then
+      s = s .. ', padding: ' .. self.padding
+   end
+   return s .. ')'
+end

SpatialConvolutionMM.lua

@@ -83,3 +83,15 @@ function SpatialConvolutionMM:type(type)
    self.fgradInput = torch.Tensor()
    return parent.type(self,type)
 end
+
+function SpatialConvolutionMM:__tostring__()
+   local s = string.format('%s(in: %d, out: %d, kW: %d, kH: %d', torch.type(self),
+         self.nInputPlane, self.nOutputPlane, self.kW, self.kH)
+   if self.dW ~= 1 or self.dH ~= 1 then
+      s = s .. string.format(', dW: %d, dH: %d', self.dW, self.dH)
+   end
+   if self.padding ~= 0 then
+      s = s .. ', padding: ' .. self.padding
+   end
+   return s .. ')'
+end

SpatialDropout.lua

@@ -41,3 +41,7 @@ end
 function SpatialDropout:setp(p)
    self.p = p
 end
+
+function SpatialDropout:__tostring__()
+  return string.format('%s(%f)', torch.type(self), self.p)
+end

SpatialMaxPooling.lua

@@ -32,3 +32,8 @@ function SpatialMaxPooling:empty()
    self.indices:resize()
    self.indices:storage():resize(0)
 end
+
+function SpatialMaxPooling:__tostring__()
+   return string.format('%s(kW: %d, kH: %d, dW: %d, dH: %d)', torch.type(self),
+         self.kW, self.kH, self.dW, self.dH)
+end