dependency free codegen

[Roger-luo]

I think mentioned by @thautwarm initially and @MasonProtter also mentioned this at some point that we can expand @match etc. to get rid of the dependency of MLStyle so we can have a much better loading time.

I tried a little bit today, here is a gist: https://gist.github.com/Roger-luo/241ee8ab360e91aefc5b8d45947050a5

the current problem is mainly about the interpolation operator $, when we unparse the Julia Expr, we aren't able to generate the correct text for $ operator. I'll left it here as an issue in case someone else wants to work on this direction.

[Roger-luo]

see Roger-luo/Expronicon.jl#13