premailer/premailer: Preflight for HTML email

For the best HTML e-mail delivery results, CSS should be inline. This is a huge pain and a simple newsletter becomes un-managable very quickly. This gem is a solution. CSS styles are converted to inline style attributes Checks style and link[rel=stylesheet] tags and preserves existing inline attributes Relative paths are converted to absolute paths Checks links in href, src and CSS url('') CSS properties are checked against e-mail client capabilities Based on the Email Standards Project's guides A plain text version is created (optional).