Handle infix operators

[andys8]

I'm trying elm-upgrade on a library that exposes infix operators. I liked how the output contains:

Here are some common upgrade steps that you will need to do manually:

I would appreciate if it would recognize the use of custom operators, which are not allowed anymore and the user to replace them by hand.

[andys8]

I found out, that the recommendations are based on the package dependencies and static. I'm not sure if it makes sense to have the information to replace operators in here for everybody, even if not using operators. This could be confusing.

https://github.com/avh4/elm-upgrade/blob/master/src/packageTransformations.js