add stylus template support

I'm having tests failing, but it seems to be due to:

1. missed libraries,
2. and some other thing I don't imagine (`\a` character),

see:

```
  1) Error:
test_can_be_used_in_a_nested_fashion_for_partials_and_whatnot(BlueClothTest):
Encoding::InvalidByteSequenceError: "\xF9" on UTF-8
  
  2) Failure:
test_renders_inline_markdown_strings(BlueClothTest) [/Users/adiaz/projects/Rubymine/sinatra-stylus/sinatra/test/markdown_test.rb:26]:
<"<h1>Hiya</h1>"> expected but was
<"<h1>Hiya</h1>\a">.

  3) Failure:
test_renders_with_file_layouts(BlueClothTest) [/Users/adiaz/projects/Rubymine/sinatra-stylus/sinatra/test/markdown_test.rb:55]:
<"ERB Layout!<p>Hello World</p>"> expected but was
<"ERB Layout!<p>Hello World</p>ap/">.

  4) Failure:
test_renders_with_inline_layouts(BlueClothTest) [/Users/adiaz/projects/Rubymine/sinatra-stylus/sinatra/test/markdown_test.rb:47]:
<"THIS.IS.<P>SPARTA</P>!"> expected but was
<"THIS.IS.<P>SPARTA</P>\a!">.

  5) Failure:
test_renders_inline_Stylus_strings(StylusTest) [/Users/adiaz/projects/Rubymine/sinatra-stylus/sinatra/test/stylus_test.rb:23]:
waiting response on how stylus can be rendered inline

960 tests, 1774 assertions, 4 failures, 1 errors, 0 skips

```

I put a pending message in fifth failure