Connection timeout

[marcbrevoort-cyberhive]

There's a connection timeout when using rusturn against a standard turn server.
I think this is due to two things.

1. create_permission does not allow setting a permission when one already exists for a given client. Thus when we want to refresh a permission, the previous one first needs to be expired completely (causing a gap in communications) By dropping the check for existing permissions, create_permission can be called again even if the permission hasn't expired yet, resulting in a refreshed permission on the server side.

2. timeouts seem to be coded backwards. For instance refresh for allocations times out at 10/9 the lifetime rather than at 9/10 the lifetime. This is probably the main issue.

[sile]

Thank you for reporting this issue.
Unfortunately, I am unable to address it at this time, as the priority of rusturn development is very low.
If you could create a pull request to fix the timeout problem, I will review it.