Changes

Implement argument capture in `@ModifyConstant` and `@ModifyReturnValue`

I'm not sure why I thought that wasn't possible while first implementing the annotations.
Regardless, this code somehow seems to work first-try, which is why tests don't crash anymore!
However on the flip side of things it seems like the allow tests are a bit flawed - so I might
have incorrectly implemented that annotation element.

There are also two other tests that fail, but I assume that those are long-standing problems
I never bothered to fix. Might be a low-hanging fruit for a potential contributor. Although
I don't think those actually exist (I know you don't exist, dear reader. Don't pretend
anything else). Uh where was I? Ah yes, the failures - I recall there having been one or two
failures for quite a while now, so I assume that this commit doesn't produce any regressions.
And on the front of the allow tests: Well I don't think it really matters whether anything
regressed as the tests wouldn't even run before this commit.
 (commit: b9bdb74)