Ref Guide: Update for *PointFields & deprecated Trie*Fields

The Ref Guide doesn't have much about Point fields, so needs to be updated since they are now default numeric types.

A few things to do:

1. Note that all Trie*Fields are deprecated.
2. Update the field type descriptions (in field-types-included-with-solr.adoc so they don't refer to TrieFields to describe how they function (like, "This works just like a Trie* field..."), since that will be less & less relevant to users as time goes on.
3. Review all the mentions of Trie fields and replace them with new configurations or descriptions that use PointFields instead.