v3: 3.98kb with schnorr. u8a-only, change names and exports

[paulmillr]

• v2: 3.99 kb gzipped, schnorr is not included because it increases bundle size
  • separate pull req implements schnorr in 4.98 kb
• v3: 3.98 kb with schnorr! 3.35 kb without schnorr

Notable changes:

• Uint8Array-only getPublicKey, sign, verify (mirrors noble-curves v2)
• Point and Signature interfaces now differ from noble-curves (negate => neg, multiply => mul)
  • curves v2 have Point.Fp and Point.Fn so it won't be 100% compatible even without these changes
• Additional utils (bytesToHex etc.) moved from etc to etc2 - TODO: better name

TODO: consider renaming coords (px, py => X, Y) for noble-curves