[#120] Add iati-identifier filter
[#120] Add unit test for  iati-identifier filter
[#120] Add last-updated-datetime filter
[#120] Add registry dataset filter
Merge branch 'master' into 120-new-filters
[#120] Add provider/receiver activity id filters
[#120] Add documentation for new filters
Merge pull request #132 from IATI/120-new-filters

Add new filters