gotypes,build: pointer dereference (#61)

Provides a method on `gotypes.Component` to allow pointer dereference. This will enable `gotypes` helpers to be used with struct pointer arguments, for example.

Updates #53 
Fixes #54

examples/args/asm.go

@@ -99,5 +99,11 @@ func main() {
 	Store(c128r, ReturnIndex(0))
 	RET()
 
+	TEXT("DereferenceFloat32", NOSPLIT, "func(s *Struct) float32")
+	s := Dereference(Param("s"))
+	f := Load(s.Field("Float32"), XMM())
+	Store(f, ReturnIndex(0))
+
+	RET()
 	Generate()
 }