add support for multiple geo points while sorting fix #1104

This utilizes the `Location` class from SolrNet to encode lat lon. 

origin: https://github.com/mausch/SolrNet/blob/master/SolrNet/Location.cs
ours: https://github.com/elasticsearch/elasticsearch-net/blob/1f8db7b8c72cc88ccedbc00bd9681f8e0f5c93d4/src/Nest/Domain/Geo/GeoLocation.cs

@mausch are you ok with us making us of it ?