enable more flexible patching like conda-build

[beckermr]

Right now rattler build doesn't have the ability to try different patch levels etc. for source code. This means that feedstocks which have patches that work with conda-build will fail with rattler-build even if the recipe is formatted correctly.

[wolfv]

Are you sure? I think we support roughly the same patch-level flexibility.

A major drawback currently is that our patch parser does fail on certain patches though because it's very strict about the format. We might wanna replace it with a more simple regex

[beckermr]

I either hit a bug or do not understand something. I will try and dig up what I found later.