Adding rewriting from HTML to DOM attributes

This is in reference to issue #5. I moved all ClojureScript code to use HTML attributes, for compatibility with hiccup and its derivatives, e.g. using `:for` instead of `:htmlFor`.

The bulk of the changes were in `sablono.compiler`, with the rest being merely updating keys across tests and other files.

After some research, I noticed there's three types of transformations between HTML and DOM attribute names:

1. The two special cases; `for` and `class`
2. Dasherized attributes; e.g. `http-equiv` and custom `data-*` attributes
3. Camelcase attributes; e.g. `onFocus`

The first category required a custom rewrite to `:htmlFor` and `:className`, respectively. The second category is handled with a dasherized-to-camelcase filter. The third category need not be handled at all, since HTML5 attributes are case-insensitive so we can just use camelcase in both HTML and DOM based code.