Handlebars Markdown Helper

The handlebars crate provides easy templating for any file type. This crate provides a helper for rendering a variable containing markdown into HTML within a temlpate.

Example

```rust

let t0 = Template::compile("{{markdown x}}".to_string()).ok().unwrap();

let mut handlebars = Handlebars::new(); handlebars.registerhelper("markdown", Box::new(::markdownhelper)); handlebars.register_template("t0", t0);

let mut m :BTreeMap = BTreeMap::new(); m.insert("x".into(), "# wow\n\n## second wow".into());

let r0 = handlebars.render("t0", &m); asserteq!(r0.ok().unwrap(), "

wow