Parse javadoc tags in xdoc generator (only @since is supported atm)

[gnodet]

This fixes new javadoc syntax:

instead of

and adds support for @since tag:

instead of

We may want to add support for more javadoc tags, but not sure which ones are used. For example the @see tag may be used, but we don't have any way to point to the actual target. All other tags (other than @since) are currently discarded.

[hboutemy]

based on recent updates in some .mdo, shouldnt' also @see and {@code xxx} be necessary?

[gnodet]

based on recent updates in some .mdo, shouldnt' also @see and {@code xxx} be necessary?

In the screen capture, you can see there's a {@code xxx} block already, so that part is covered.
For the @see, I don't think we can generate a link in the xdoc. That's why I left it out, but we could generate something like the output of @since without the link though... ?

@hboutemy ?