Working with mardown v2.3.1, and some updated options.

Got this working again for markdown version 2.3.1 (latest code from github and from pypi doesn't work with latest markdown, primarily due to issue #1, but some other minor issues as well).

-Fixed issue #1 (import error): etree is under markdown.util, not just markdown.
-Made use of intPixelSize config.
-Removed unused intCanvasSize config.
-Made use of Pattern's default impl of getCompiledRegExp, which wraps the pattern in some important regex.
-Added alternate syntax which is more general and allows specifying options per use (colors, size, and error correction level).