This commit introduces a private data() array, and a public method for classes that extend Base to call to setup the defaults.

This is necessary to make sure that all default class variables make their way into the data array so that magic methods can access them like they can any other variable.

This commit is necessary to make sure that all object properties are correctly setup in the private data array.

* Change from array to object
* Introduce unset_vars() to parlay off of set_vars()
* Introduce validate_key() to reduce some code duplication in magic methods
* Switch from is_callable() to method_exists() so that it works as intended with __call()
* Make sure magic un/set methods operate on the correct variables
* Avoid setting object array keys directly, triggering byref debug notices
* Some general code & docs improvements to related methods
* Add 'join' to query & request clauses