feat: Improve #tokens method (#66)

spec/blueprint/html/helpers_spec.cr

@@ -4,7 +4,7 @@ private class ExamplePage
   include Blueprint::HTML
 
   private def blueprint
-    div("Tokens", class: ["a", "b", tokens({->c? => "c", ->d? => "d", ->e? => "e"})])
+    div("Tokens", class: ["a", "b", tokens(c?: "c", d?: "d", e?: "e")])
   end
 
   private def c?

src/blueprint/html/helpers.cr

@@ -1,12 +1,12 @@
 module Blueprint::HTML::Helpers
-  def tokens(conditions : Hash(Proc(Bool), String)) : String
+  macro tokens(**conditions)
     String.build do |io|
-      conditions.each do |proc, classes|
-        if proc.call
+      {% for key, value in conditions %}
+        if {{key.id}}
           io << " " unless io.empty?
-          io << classes
+          io << {{value}}
         end
-      end
+      {% end %}
     end
   end
 end