I want to be able to get all keywords for a specific URL.  While the function yourls_get_duplicate_keywords() exists, it returns NULL -- instead of a single keyword -- if yourls_allow_duplicate_longurls() is false.  This commit refactors the keyword logic from yourls_allow_duplicate_longurls() into yourls_get_keywords() so a keyword list can be obtained regardless of the state of YOURLS_UNIQUE_URLS.
Added sort (order by) options to new yours_get_keywords() function.
Clarified comment.
Moved filter into named function.
Fixed Travis error.
Updated function name. Deprecated old version. Updated yourls-infos.php.
Added filter to yourls_get_longurl_keywords. Fixed typo.
Fixed typo.
Function yourls_get_longurl_keywords() to simplify logic between having duplicated keyword or not
Merge branch 'master' of https://github.com/YOURLS/YOURLS