Handle method calls on pointer receivers

[kalexmills]

Another way a pointer from a range loop can be passed into a function is via a pointer receiver. Currently this is ignored, but it can also lead to issues in cases where the pointer receiver is written elsewhere in memory or used inside a goroutine.

[kalexmills]

This will require:

1. Inspecting for SelectorExpr and doing (a very simple) name resolution to find pointer arguments passed into functions on the LHS of the .
2. Modifying the callgraph to include functions with pointer receivers as part of the the signature of function declarations.
3. Modify pointerescapes to know whether a CallExpr is contained within a SelectorExpr, and look up the signature accordingly.

It is still the case that no type-checking needs to be performed here.