Add normalized comparison to check sessions (#396)

[dpalmasan]

First of all, thanks for this amazing tool, I started to use it recently (I come from the tox world)

This is a possible fix for (#396):

• Attempt to do the previous checks
• On fail, it will normalize arguments using ast (based on discussion)
• The comparison will be on ast representation of the strings
• Add unit tests

[theacodes]

I like this approach a lot! Thank you!