Progress on: #535

* Use BufReader and BufWriter

* Add TODOs

* `decl_storage!` exposes json metadata about the storage

The metadata can be accessed by calling `store_json_metadata()`.

* Hide internal macros in the documentation

* Include the function documentation in the store json metadata

* Adapt the storage declarations to use doc comments

* impl MaybeEmpty for H256 and u64 (aka AccountId in prod/tests)

* binaries

* DigestItem trait

* removed autoimpl in impl_outer_log

* StubDigestItem -> ()

This reverts commit ad89579f.

This reverts commit 7c18bb60.

* Fetch parity-common dependencies from crates

* Update triehash

* Fix code to fit latest triehash
Fetch kvdb-rocksdb from crates

* type params

* lockfile

* lockfiles

* wasm binaries and lockfile

* Somerhing wrong.

* My attempt to fix

* cfg_attr for serde

* Fix tests