efbytesref of 20140717, move Elias-Fano code to eliasfano package

efbytesref as of 20140717

LUCENE-5524

This closes #60

Update to recent trunk, and move all Elias-Fano classes into a separate package o.a.l.util.packed.eliasfano. The existing EliasFano* classes are restored to trunk, the packed.eliasfano package can be merged back into  the packed package later.
Otherwise no changes to pull request 60.

The idea is to prepare a port to 4.9.0 and/or to prepare compilation into a separate jar.