elasticsearch-aknn-v0.0.4

Added new rest endpoins:

• _aknn_search_vec
• _aknn_clear_cache

And new arguments to _aknn_search and _aknn_search_vec endpoints:

• rescore
• debug
• minimum_should_match
• filter

Plugin tested and confirmed working for ES 6.5.1. Other ES versions listed here should work, but not tested.