Add Ant targets for texinfo documentation
Add Ant targets for texinfo documentation

By default, we now build the specification in texinfo format in addition
to PDF, HTML, and single HTML. In addition to that, the
lang.docinfo.install target can be used to install the specification
into the system's info directory.

gijsleussink/ceylon,gijsleussink/ceylon,gijsleussink/ceylon,gijsleussink/ceylon,gijsleussink/ceylon