v0.5.1-theano

Difference between 0.4.0 and 0.5.0 is functionality added to support separate treatment of positive and negative contributions for all activation functions (the "RevealCancel" rule - matches functionality in ICML submission). Difference between 0.5.1-theano and 0.5.0-theano (for which a release was not drafted) is that some support was added for border mode same and a cast to float32 was added to the integrated gradients function to account for cases where the supplied data might be uint8.