Added StringLiteral#captialize in macros

spec/compiler/macro/macro_expander_spec.cr

@@ -191,6 +191,10 @@ describe "MacroExpander" do
       assert_macro "", %({{"hello".upcase}}), [] of ASTNode, "HELLO"
     end
 
+    it "executes capitalize" do
+      assert_macro "", %({{"hello".capitalize}}), [] of ASTNode, "Hello"
+    end
+
     it "executes lines" do
       assert_macro "x", %({{x.lines}}), [StringLiteral.new("1\n2\n3")] of ASTNode, %(["1", "2", "3"])
     end

src/compiler/crystal/macros.cr

@@ -471,6 +471,8 @@ module Crystal
             raise "wrong argument for StringLiteral#[] (#{arg.class_desc}): #{arg}"
           end
         end
+      when "capitalize"
+        interpret_argless_method(method, args) { StringLiteral.new(@value.capitalize) }
       when "downcase"
         interpret_argless_method(method, args) { StringLiteral.new(@value.downcase) }
       when "empty?"