Example header/2

header/2
Merge pull request #6 from fooflare/master

Renamed render_fun as body_fun to avoid compile error
Merge branch 'master' of git://github.com/stuart-thackray/NitrogenProject.com into stuart-thackray-master
Clean up content-type demo a bit, make clearer

Also added some comments, and removed unnecessary binary_to_list/1
conversion from demos_contenttype_image.erl
Add more explaination to the contenttype demo
Clarified text for header/content-type demos