Lint/UnusedArgument: fails to recognized used argument inside macro

closes #117

spec/ameba/rule/lint/unused_argument_spec.cr

@@ -228,6 +228,21 @@ module Ameba::Rule::Lint
         )
         subject.catch(s).should be_valid
       end
+
+      it "doesn't report used args in macro literals" do
+        s = Source.new %(
+          def print(f : Array(U)) forall U
+            f.size.times do |i|
+              {% if U == Float64 %}
+                puts f[i].round(3)
+              {% else %}
+                puts f[i]
+              {% end %}
+            end
+          end
+        )
+        subject.catch(s).should be_valid
+      end
     end
 
     context "properties" do

src/ameba/rule/lint/unused_argument.cr

@@ -55,7 +55,7 @@ module Ameba::Rule::Lint
 
     private def find_unused_arguments(source, scope)
       scope.arguments.each do |argument|
-        next if argument.ignored? || scope.references?(argument.variable)
+        next if argument.ignored? || scope.references?(argument.variable) || argument.variable.used_in_macro?
 
         name_suggestion = scope.node.is_a?(Crystal::Block) ? '_' : "_#{argument.name}"
         issue_for argument.node, MSG % {argument.name, name_suggestion}