added tests; completed incremental sync

get_page_of_events - returns list of events for a given page; can
turn on/off etag

get_changed_page_urls - returns list of urls for all pages that
have changed since last sync

update_indices - update the indices for all pages that have changed
since last sync
Merge github.com:cfpb/github-wiki-search

Conflicts:
	sync.py
fixed empty events list handling
Merge pull request #2 from dgreisen-cfpb/master

sync