Add support for hidden services v3

[thelegy]

Tor now has support for hidden services v3 for quite a while. This library lacks support for it.

Note: This code exits because I needed a rather quick solution. I would vote for a cleaner solution that is a little more effort. This PR, although being functional, does not feel like the proper solution to the problem.

This PR adds basic support for hidden services v3. To aquire this it applies the following changes:

• It changes the mapOnion function to create a hidden services v2 key if no secret key is given.
• Additionally to the mapOnion function it adds another mapOnionV3 function that implements the same behaviour for hidden services v3. Also tests are duplicated for this function.
• The accept function now uses mapOnionV3.

The latter one is kind of a breaking change as accept is not able to cunsume hidden services v2 keys any longer. But duplicating accept felt somewhat wrong to me.

Mid term I would vote for rewriting this library a bit and utilizing its own types for the keys. This would deduplicate mapOnion and mapOnionV3 again and also would empower accept to work with hidden services v2 again.