Removed unnecessary margin

This is already set by our reset and setting it again makes reusing our
defaults a little annoying in the editor styles
Added editor styles

Woohoo! This is our first stab at including editor styles in Compass.
We probably can abstract this out a bit more so that the build can
reuse more of the actual theme styles without having to copy them in
manually, but this is a good starting point. Related to #23
Updated the build process to handle editor styles

This makes sure our editor styles are pulled into the theme when we run
the `grunt build` command without slowing down our normal `grunt` and
`grunt watch` commands.
Removed static max width refrences

We’re now reusing the $max-width variable wherever possible to make
changing the global layout settings a bit easier.

This would probably be more useful if we switch to ems or some unit of
measurement other than pixels. Props to @ccgjosh for pointing this out.

Closes #24
Improved doc styling and organization

I also moved in some items that were previously in _layout.scss but
didn’t really fit. At some point, _misc.scss will likely need some more
attention