Add support for out-of-body script tag in HTML

- For symmetry with the s-expression syntax, HTML syntax files may have
  a script tag preceeding the html document. This script tag must
  contain the namespace declaration and, optionally, any number of other
  cljs expressions.
- The values of cljs expressions in the out-of-body section will not
  appear in the DOM, unlike the values of cljs expressions that are in
  script tags in the body.
Merge branch 'master' of github.com:tailrecursion/lein-hoplon