Adding doc about custom purge rules. Closes #81
Adding doc on how to auto hydrate fields when updating a record. Based on #78, closes #77
Using `Eloquent::fill()` to hydrate model

The old method relied on validation rules, meaning that properties that were not validated would not be populated when the model is configured to be automatically hydrated.
Documentation was changed to reflect this behavior, and also to explicitly explain the differences between forced and automatic hydration.
This references #77 and #78 and closes #51
updateUniques now has a bit more flexibility, Reflection methods removed from buildUniqueExclusionRules