Implement arguments case equality

Implements https://github.com/icy-arctic-fox/spectator/issues/47
Some specs are failing and need to be resolved before the new feature is considered done.

spec/issues/github_issue_47_spec.cr

@@ -11,7 +11,7 @@ Spectator.describe "GitHub Issue #47" do
 
   let(fake) { mock(Original) }
 
-  xspecify do
+  specify do
     expect(fake).to receive(:foo).with("arg1", arg2: "arg2")
     fake.foo("arg1", "arg2")
   end