lint: enable golint

Enables golint and fixes function naming errors (operand checks
incorrectly cased).

Fixes #10

internal/gen/avotypes.go

@@ -19,5 +19,5 @@ func implicitRegister(t string) string {
 
 // checkername returns the name of the function that checks an operand of type t.
 func checkername(t string) string {
-	return "operand.Is" + strings.Title(t)
+	return "operand.Is" + strings.ToUpper(t)
 }