* allow ordering using columns from object relationships, close#463
* validate table fields in nested insert
* add tests
* add docs
* change 'table_order_by' type from enums to ordered map
* remove unwanted code from 'Schema.hs' file
* 'AnnGObject' is not list of field name and value tuple
* update docs for new order_by type
* use 'InsOrdHashMap' for 'AnnGObj'
* handle empty fields in order_by
* remove '_' prefixes for asc/desc
* fix the changed order_by syntax across the repo
* fix primary key changing on upsert, fix#342
* add 'update_columns' in 'on_conflict' object, consider 'allowUpsert'
* 'ConflictCtx' type should respect upsert cases
* validation for not null fields in an object
