added lux_docid for cloud document ordering
docLimit was off by one
Merge branch 'cloud' of https://github.com/msokolov/lux into cloud
adding IDField so it can be indexed
IDField models the lux_docid we use for document ordering now since
Lucene docid is not usable in cloud solr land (or really in solr alone,
either).  In this commit, we add the update processing needed to
generate these ids along with the supporting field definitions.
first basic happy path test of cloud operation now passes!