Coalesce shorthand classes into attributes

Shorthand classes are prepended to attribute if provided.

- Addresses machty/emblem.js#78

It's a bit hacky but it allows syntax like `div.shorthand-class class=var`

Flow is as follows:
If there are inTagMustaches, script tries to find if there is bind-attr node and that has class binding and prepends to it.
If that fails, it tries to find if there was simple binding `div.foo class=boundVar` and converts that to bind-attr mustache node and prepends shorthand classes to it.
It also supports `div.shorthand class="in-attr"` merging.

Shorthand classes are always prepended.