#306 relative HTML links

[Mark Edgington]

It would be very nice if one were able to specify
relative HTML URLs for articles which are stored on the
local filesystem.

In other words, assume that the .bib file is in a
directory which also contains a "MyHTMLSite" directory.
Inside of the "MyHTMLSite" directory is an index.html
file. Now, what would make sense is to allow the user
(somehow) to specify that a URL is relative, and the
URL field would simply contain "MyHTMLSite/index.html".
Then when the 'launch-url' icon was clicked on for an
article, it would convert this URL to an absolute URL,
and pass it to the browser.

Or perhaps, a "Main HTML directory" option could be
added (in addition to the already existing PDF
directory and PS directory options) in the program
preferences, and this path would be prepended to the
relative URL specified in the URL field of an article.