Caching information about definitions of differing macros

[PLukas2018]

First part of commits from #314 . This PR adds:

• caching of Syntax difference kind (because there can be multiple kinds of syntax differences - macro, assembly, macro-function, function-macro) -- I think it could be useful to have this saved in Python, personally I used this information for visualisation of function-macro/macro-function differences in the result viewer, but right now I am thinking it is not absolutely necessary because I should be able to deduce this based on names of the differing 'objects', but I am still thinking it could be useful to have it.
• caching of the definition of differing/last macro in Syntax difference -- this is useful for showing code/differences of the macro in the result viewer.

I will reference comments/questions from #314 which are relevant to this PR.