Refactor fields for index to support nesting
Better handle nulls in index requests
Tidy index tests
Allow arrays to be specified as Seqs
Document index changes
Update to use variadic tuples instead of a Map
Remove use of procedual syntax for functions
Allow explicit FieldValues when indexing

For when the implicit Map/Seq conversions don't work.
Also opens up the possibility for custom FieldValue implementations.
Merge pull request #118 from stringbean/refactor-index-fields

Refactor index fields