This allows mime types in the form text/html, text/*, or */*
This required a few minor test/code changes where previously nil was
used as a mime string.
Templates only have one format. Before this commit, templates would be
constructed with a single element array that contained the format. This
commit eliminates the single element array and just implements a
`format` method. This saves one array allocation per template.
Before we were calling to_sym in the mime type, even when it is unknown
what can cause denial of service since symbols are not removed by the
garbage collector.
Fixes: CVE-2014-0082
