Fix markdown parser

[gossi]

With version 0.6.0 and using angle bracket syntax inside your markdown files will actually brake the build.

This is not working:

<DocsDemo @class="docs-demo" as |demo|>
  {{#demo.example name='demo.hbs'}}
    <FooBar @label="fubar"/>
  {{/demo.example}}

  {{demo.snippet 'demo.hbs'}}
</DocsDemo>

This patch fixes the parser to not only handle curlies but also angle brackets :)

[samselikoff]

Ty!

[miguelcobain]

I think this broke something.

When I write a paragraph like this in my template.md:

Up until now the guides assumed you passed in an array of data to the `@data` argument of `<YetiTable>`.

the result is

However, if I change <YetiTable> to YetiTable> it works fine:

So, the opening < is making things look unformatted. Basically everything gets stuck inside a single <p>.