Differentiating doc from apidoc

This renames the doc task to apidoc.  The apidoc delegates to jsdoc3 currently.  We will have additional documentation that is not built by jsdoc3.  It makes sense to reserve the more general 'doc' name for building all documentation (not just apidoc).
Merge pull request #1054 from tschaub/apidoc

Differentiating doc from apidoc.
New font and header background color

This matches the website design of the new-build branch of
openlayers.github.io better.