allow nil value for date type codec
Merge pull request #20 from bterkuile/ace48fcbd4558cc7d717a8e6309afa4d4f9c3033

Allow date values to be nil when specified :as => :date
lazy load queue writers (beanstalk_writer, resque_writer) when needed
change log / gem spec updated
removed dependency on xapian-ruby
index writer specs fixed
examples extended / refactored
added missing spec
added a reindex rake task
DocumentBlueprint.setup and DocumentBlueprint.blueprint_for accept symbols and strings; class arguments are deprecated
lazy model extension
DocumentBlueprint.base_query expects a block; passing the query as an argument is deprecated
data mapper support for lazy model extension
updated example configs to new conventions
added missing specs
updated the change log
renamed the reindex rake task
updated the change log
load data mapper model extender only if needed
Gemfiles in rails examples updated