Specify package files in Cask
Ignore the dist package generated by Cask
Update the Makefile to use new Cask 0.6 features

Cask will build our package now, including the info files, so we don't
need our own stuff anymore.  Hence we drop our own info and package
targets.

We also refactor and improve the makefile to make the target name a bit
more consistent.
Update the manual