Wrapper for BLS python bindings in Chia Network

### What is wrong?
To address https://github.com/ethereum/py_ecc/issues/66, we can make use of faster implementations. Chia-Network has BLS signature [implementation](https://github.com/Chia-Network/bls-signatures) in C++, as well as its [bindings](https://github.com/Chia-Network/bls-signatures/tree/master/python-bindings) for Python.

### How can it be fixed
To make use of the bindings, we need a wrapper for the essential functions in `bls.api`
- `sign`
- `privtopub`
- `verify`
- `aggregate_signatures`
- `aggregate_pubkeys`
- `aggregate_multiple`

### Possible concerns
[Chia-Network/bls-signatures](https://github.com/Chia-Network/bls-signatures) is under the license Apache 2.0. From my understanding, since we only import the library, from the rules in Apache 2.0, it seems not to affect our license. Is it correct? I don't have enough experience in the licenses. Please correct me if I'm wrong.

Start with py_ecc issue 66 and the Chia-Network bls-signatures Python bindings, especially the `bls.api` entry points. Determine how to wrap `sign`, `privtopub`, `verify`, `aggregate_signatures`, `aggregate_pubkeys`, and `aggregate_multiple`, and clarify the Apache 2.0 licensing concern. Done means the essential functions are available through the wrapper with the licensing question resolved.

Written by the indexing model from the issue text.