* WIP
* Iteration over all keys with the specified prefix
* Add clear_prefix in runtime-io
* Introduce a custom storage impl: Double Map
* Remove prefix
* Impl for_keys_with_prefix for light client
* Fix wasm_executor
* Test storage removal leads to removal of stroage
* Check for ok result in storage tests.
* Add docs.
* Remove commented code under decl_storage!
* Add clear_prefix test in runtime-io
* Add test for wasm_executor
* Prefix walking test.
* Rebuild binaries.