Update (post.html) with HTML5 semantics.

HTML5 article element should wrap all article contents (header, h1,
image,..)
[Update/Add] Initial Stylus mobile layout/design

update:
* (_source/_assets/stylus/global/base.styl)
* (_source/_assets/stylus/global/configuration.styl)
* (_source/_assets/stylus/main.styl)

add:
* (_source/_assets/stylus/modules/footer.styl)
* (_source/_assets/stylus/modules/header.styl)