implement hyperref colorlinks (?)

[xworld21]

hyperref uses color to distinguish among citations (green), cross references (red), external links (magenta), and a few others when given the option colorlinks. LaTeXML currently ignores colorlinks and the associated options linkcolor, anchorcolor, citecolor, filecolor, urlcolor, allcolors (and also menucolor, runcolor but they seem PDF specific).

[dginev]

It would be great if the solution here allows for restyling in CSS by using class names - rather than setting the concrete original colors in style attributes.

Enabling downstream themeing in CSS is a meta-goal I have, and is particularly relevant to upgrading "legacy" documents, that were written without HTML in mind.