fix for #147, add macro identify

spec/compiler/macro/macro_expander_spec.cr

@@ -261,6 +261,11 @@ describe "MacroExpander" do
       assert_macro "", %({{[1, 2, 3].empty?}}), [] of ASTNode, "false"
     end
 
+    it "executes identify" do
+      assert_macro "", %({{"A::B".identify}}), [] of ASTNode, "\"A__B\""
+      assert_macro "", %({{"A".identify}}), [] of ASTNode, "\"A\""
+    end
+
     it "executes join" do
       assert_macro "", %({{[1, 2, 3].join ", "}}), [] of ASTNode, %("1, 2, 3")
     end

src/compiler/crystal/macros.cr

@@ -557,6 +557,8 @@ module Crystal
         interpret_argless_method(method, args) { StringLiteral.new(@value.downcase) }
       when "empty?"
         interpret_argless_method(method, args) { BoolLiteral.new(@value.empty?) }
+      when "identify"
+        interpret_argless_method(method, args) { StringLiteral.new(@value.tr(":", "_")) }
       when "length"
         interpret_argless_method(method, args) { NumberLiteral.new(@value.length, :i32) }
       when "lines"