T4json

* Added `multi_iter()` method to T4Json instance so that multiple variables can be looped through the data at the same time.
* Also added `multi_iter()` as a global function.
* Cleaned up code and made it just a bit faster.
* The dunder methods of the T4Json class were improved.

* Added types() method to T4Json instance.
* Added convert_singular_lists() method.
* Added **_convert_singular_lists_** parameter to flatten() method.
* The flatten() method should generally be up to 15% faster.
* The **_chain_key_include_index_** of the flatten() method was fixed/improved.
* cleaned up code in internal methods.

* Added support for re-calling T4Json instances to load new data.
* Changed the chain_key parameter to chain_keys within the flatten() method.

* Slicing Operations now supported on T4Json instances.
* Support for adding and subtracting items or pairs to/from T4Json instances.
* Support for iterating through a T4Json instance.
* Support for getting the length of a T4Json instance - (number of all the pairs/items on the first level).
* Support for checking equality (of data) between two T4Json instances.
* Support for checking in-equality (number of all the pairs/items on the first level) between two T4Json instances.
* Default support for printing a T4Json instance.
* Adding a pretty print method.
* Cleaned up code.

- Greatly improved the error messages.
- Fixed t4json.save() method.
- Improved **_t4json_**`.load()` & `load_file()` & `load_from_url()` & `load_from_string()`
- Added t4json.load_object() for loading python objects.
- Added new parameters to **_t4json_**`.load_from_url()` for making `POST` (and others) requests. Also added support for headers and body.
- Improved walking up levels in nested data using paths.
- Improved support for key paths to work with non-string objects that are keys.
- Cleaned up code in general.