Avoid running out of memory and clear object cache between pages in index_helper

Experiencing fatal out of memory messages, thought this would be a useful addition. Kept dying at about 11k posts, now able to consume all 21201 posts.
Add support for order and orderby arguments. Basic support provided for sorting by post_title and post_name
Add tests for all added order and orderby cases
Separate out is_alive and is_activated checks into separate method
Merge branch 'sc0ttkclark-patch-1' into develop
Merge pull request #146 from 10up/bugfix/is-alive

Separate out is_alive and is_activated checks into separate method
Update @since docblock mentions. Correct post_title and post_name to use title and name arguments - match WP_Query arguments.
Update readme to instruct on usage for orderby and order parameters.
Merge pull request #144 from 10up/feature/orderby

Add support for post_title and post_name orderby parameters. Add support for order parameters
Fix incorrect prefix and variable in parse_orderby
Fix mislabeled orderby
Merge pull request #147 from 10up/bugfix/orderby

Fixes incorrect prefix placement for sort array
Add raw map for post_title; fix tests for ordering.
Remove debugging lines that accidentally made it in
Merge pull request #149 from 10up/bugfix/order-remap

Add raw field to post_title, fixes specific ordering issues.
Credit to Automattic and Alley Interactive for code
Clean up / refactor elasticsearch, alive, index exist checks. Fixes #150
Add some @sinces and docbloc items
Merge pull request #151 from 10up/feature/clean-up-checks

Clean up exist/alive/activate checks.
Increment version to 1.1; remove stable version and contributors list