Meta fields were locked down to not allow exotic options to the
underlying field types in #8143. This change fixes the docs
to no longer refer to the old settings.
closes#10879
_id and _routing now no longer support the 'path' setting on indexes
created with 2.0. Indexes created before 2.0 still support this
setting for backcompat.
closes#6730
Ryan Ernst
dtpeacock
Clinton Gormley