Add borsh serialization support to primitive types

[sloboste]

Add the ability to serialize the H* and U* types using borsh

[ordian]

Hey, thanks for the PR!

1. There's an open discussion whether we want it here: #640
2. If the answer to 1 is "yes", we don't need to introduce "impl-borsh", instead just use derive gated the same way as scale_info.

[sloboste]

Ah, didn't see that issue - thanks for pointing it out @ordian.

I'll drop a comment in https://github.com/paritytech/parity-common/issues/640