naive impl bls signature and vrf

[zhenfeizhang]

Description

closes: #XXXX

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[zhenfeizhang]

This is a naive implementation of bls signatures and vrfs. using an inefficient way to hash element to the group.
There are a couple of todos:

• implement aggregation and batch verification
• implement ieft hash to group

For now we want to know if the APIs are sufficient for your need @nmccarty

[chancharles92]

LGTM

[zhenfeizhang]

Just realized that arkworks has already implemented the standard hash_to_curve. So one less thing we need to do.

https://github.com/arkworks-rs/algebra/blob/master/ec/src/hashing/curve_maps/swu/mod.rs