Omid Bodaghi

Add error/keypair modules and documentation for VRF crate (based on #1794)

1

**Summary** This pull request adds the following to the draft proposed by [@carloskiki](https://github.com/carloskiki) in [#1794](https://github.com/RustCrypto/traits/pull/1794) to the issue [#1728]: - **Error Module**: Introduced a dedicated error type and improved error...