Gaussian shape and gaussian edge

[MatthieuDartiailh]

Adding a gaussian shape for analogical pulse would make sense. The width can be specified in a different ways : standard deviation, width, etc ... I would be in favor of a switch to select the in put method.
I also wonder if this could be merged with a pulse shape with gaussian edge. We would need some way to detect that constant values need to be added in the middle.
Thoughts @ncottet

[MatthieuDartiailh]

@leghtas could you make a PR with your tanh and gaussian shapes ?

[leghtas]

Done