Add an option to trim whitespace from rendered HTML.

Add an option for trimming the generated HTML, which will do the following:
 * Remove all leading & trailing whitespace on every line
 * Remove all empty lines
 * Attempt to keep formatting inside < pre > < /pre > tags

This is fairly safe unless "white-space: pre;" is used in css for formatting. Since there is no way to detect that, you will have to keep trimming off in these cases. 
(just spitting out my thoughts here)

This is safe because a false positive, at worst, will cause some spaces to not be trimmed.