* factorization
* introduce GenericUnhashedStorage
* implement generator and storage
* impl double map in storage macro
* improve StorageDoubleMapXX methods
* remove storage from example and impl test
* remove old comments
* wasm compatible
* improve imports
* rename storages
* update runtime impl version
* make code less verbose
* impl hash config for second key in double map
hash available are all of Hashable trait
* use double map in decl_storage for contract
* fix double map config issue
* add hasher into metadata
* update impl version and build wasm
* doc
* add attrs
* update metadata version
* update runtime version
* fix unused storage