Pin encoding into aeser

[klercker]

Moved the pin encoding/decoding methods from core to serialization. A follow-up PR will be done post merge for the corresponding refactoring in aeternity/aeternity

This pull request is supported by the Æternity Foundation.

[hanssv]

Moving this to aeserialization is 100% the right move 👍

But, I would like this to be less prominent, i.e. in a separarte module. And it should be made much more clear that this is HyperChains stuff!

[klercker]

So, proposing to do this:

1. introduce aeser_hc.erlmodule
2. Move the methods there
   ...and then we have ourselves a merry little Christmas 🎄 (in a week of course...)