Support superclasses with any expression

[marcoroth]

As raised in #41 we should somehow support superclasses that have an expression opposed to just referencing a constant. For now we return nil for unprocessable superclasses.

Some solutions might include, but are not limited to:

a) show that we couldn't analyze the superclass
b) show the "raw" expression
c) try to statically trace the expression (this only works to some degree though)
d) try to parse it out of the docs