The Export format version is set to 0.1
Long term keys are not exported.

This makes it much easier to export/import the crypto state.
In preparation for implemeting import/export of context.

Free RC4 state if any
Free workstations tring if any

Also make sure to safely zero the struct before freeing to avoid leaking any
key material.

There is no need to copy creds around, they are always available
or retrievable.

Thanks to Stefan Becker <chemobejk@gmail.com> for finding this leak.

Can't use ':' in the prefix name as ':' is the separator between prefix and
values.

Also add simple sanity check test.