Merges v1.1.2 updates from http://wordpress.org/plugins/search-filter/
Updates README with latest changelog
Adds date filtering using a simple text input
Adds support for date ranges
Uses HTML5 date input type
Fixes query for a single date
Fixes empty date filtering
Removes extra label tag from date input
Adds wp_dropdown type for displaying indented hierarchy
Adjusts styling a bit
Merge pull request #1 from bradaric/master

Updated to latest version, added support for post_date filtering, added hierarchical selects, bug fixes