This changes how the liquid integration works. It now integrates the Textile
conversion step. This was necessary because if you first convert the snippets
inside of loops and conditionals from Textile to HTML, you loose some
important context information which is required to e.g. build proper lists in
textile.

We expect the standard case that Liquid tags return Textile markup instead
of HTML. Thus, we can convert the final textile markup to HTML as a very last
step.

To allow existing and new macros (or tags) to return HTML for advanced usage,
we save their respective output into the context and put a placeholder string
into the generated markup. After the transformation to HTML, we insert the
previously generated HTML into the string using search+replace in
lib/chili_project/liquid/template.rb. Tags have to be registered using
:html => true for this special treatment.