split __init__.py to multiple moduels.

Author: jchen293

.flake8

@@ -1,3 +1,4 @@
 [flake8]
 max-line-length = 120
 extend-ignore = E203
+per-file-ignores = __init__.py:F401

CHANGELOG.md

@@ -9,6 +9,8 @@
 * Adds Python version to user-agent header on requests
 * Removes `shipment.get_rates()` method since the shipment object already has rates. If you need to get new rates for a shipment, please use the `shipment.regenerate_rates()` method.
 * Add `retrieve_me()` convenience function that allow users to retrieve without specifying an ID.
+* Remove `blob` class since it's never being used
+* Remove `track_with_code` in shipment class since it's no longer being used
 
 ### v6.0.0 2021-10-12