Treatment of <code> blocks #96
Description
The MarkupEditor does not treat <code> as a block element, since it's not one. It does, however, have markup.css set up to format code inside of <p> and other "style" block elements differently than when <code> is inside of a <blockquote>, which is a block element itself. For <p> and the other "style" elements, it <code> uses css "display: inline", while outside of the "style" elements (e.g., in <blockquote>) it uses css "display: block". This kind of works, but it means that in the MarkupEditor currently, the only time you can get code to display as a block is in an indented block, which is not what everyone (including me) wants. To fix this, I think <code> needs to be displayable inside of a <pre> block element. This in turn will require special handling for Enter and for multistyle operations.
An associated problem with <code> formatting is that it needs to be scrollable horizontally. This is fixable by including "overflow-x: scroll" in code's css. However, given the other problem above, the scrolling only works currently when code is in a blockquote, since the css uses "display: inline" inside of the styling elements.