Introduce higher level data types

[axic]

For the types:

• Address (160 bit)
• EtherValue (128 bit)
• StorageKey (256 bit)
• StorageValue (256 bit)
• Hash (256 bit)

It should not pull in any big dependency and there's no need to have an operators on these, only to wrap the underlying data type and expose some basic traits (as_slice, to_vec).