Hi,

I think htmlize.el should be optional for ox-html. Although htmlize.el
is cool, there are still reasons to don't use it, e.g.,

- Colors looks nice in Emacs looks bad in the web browser
- No color at all in batch mode
- I want to use third party solutions such pygmentize and highlight.js

When user sets org-html-htmlize-output-type to nil, don't use
htmlize.el.