correctly detect indirect uses of reflection

[lu4p]

(see commit message)

[lu4p]

@mvdan added some docs and support for composite literals

[mvdan]

Before I do another round of review - did you benchmark this? I generally assume that bug fixes come before performance, but this go/ast analysis is adding two more ast.Inspect calls and one is nested, so I'm somewhat worried that this will negatively affect build times.

[mvdan]

Another reason for (slight) worry is that you seem to be tracking most forms of assignments via either foo = bar or foo: bar, so that will likely be quite a lot more book-keeping for code being obfuscated.