* Add methods to PrefixIterator to support iterating from a specific key
* Expose the decode functions used in iterators for storage maps
* Use associated decode function in tests
* Revert "Expose the decode functions used in iterators for storage maps"
This reverts commit 34f57d92db89646d0c98ea1880df58d58e523b09.
* Fix documentation for next_key
* Add API for iterating from a specified key for all storage map types
* Enhance pagination test
* Add API methods to storage map types
* Rename next_key to last_key
* Rename last_key to last_raw_key
* Specify that iteration starts after starting_raw_key
* Update documentation on iteration ordering
* Rename next_key to previous_key
* Enhance pagination unit test
* Create unit tests for all kinds of iter_from methods
* Define iter_from in terms of iter rather than vice versa
* Cargo fmt