Up version to 0.4.0-beta.2

Release v0.4.0-beta.1

Release v0.3.3

Release v0.3.2

Release v0.3.1

Released v0.3.0

Release v.0.2.0

Adds AsRef<[u8]> and From<&[u8]> for AsString if the content supports…

… them.

Adds missing trait derives for the AsString encoding wrapper.

This should allow to restore byte types encoded with the AsString
helper even in places where they specific traits are required
e.g. as key for a HashMap