add ePub support

[stliu]

docbook 1.74.0 does support epub

[sebersole]

We just need to add the appropriate org.jboss.jdocbook.util.StandardDocBookFormatMetadata entry for an epub FormatMetadata

[emmanuelbernard]

This is a bit more complicated, when I tried the META-INF as well as the other epub directory required were created in current dir rather than the target dir, (this was with 1.72 so this might not be true anymore)
Also the split files should be zipped into a .epub file (zip format) and a mimepart might be needed

See http://www.ibm.com/developerworks/xml/tutorials/x-epubtut/section5.html for some info

[stliu]

yes, they are created in current dir, that property is defined in the epub xsd, and re-set that value does not work
still trying to find a way to fix it
and I already done some initial work on this task, the zip and mimepart things are not problem anymore
just can't find more time on it for now...