Draft PoC version for devnet (v0.0.1)

What's Changed

• Add DPoS contracts & unit tests for devnet by @ducthotran2010 in #1
• Update devnet config by @ducthotran2010 in #2
• Update README.md by @ducthotran2010 in #3

Notes

• This version includes getting candidates, filtering unqualified validator candidates and sorting on the contract RoninValidatorSet.
• This version does not include the methods to prevent the 51% attack. It is not finalized at the implementation time.
• All configurations can be found in config.ts.

New Contributors

• @ducthotran2010 made their first contribution in #1
• @nxqbao made their first contribution in #1

Full Changelog: https://github.com/axieinfinity/ronin-dpos-contracts/commits/v0.0.1