add aPlonK

this adds the aPlonK cryptographic method alongside Semi-AVID and KZG+.

changelog

• new feature aplonk:
  • the algebra module is compiled when either kzg or aplonk features are enabled
  • algebra::scalar_product_polynomial compiles only with kzg
  • the other algebra::* functions compile with aplonk
• u32_to_u8_vec has been moved to new conversions module which compiles when either kzg or aplonk features are enabled
• new aplonk module which compiles only when the aplonk feature is enabled
  • public structures
    • Block
    • Commitment
    • SetupParams
    • VerifierKey
  • public functions
    • setup
    • commit
    • prove
    • verify
  • internals
    • ipa::Params
    • ipa::Proof
    • ipa::prove
    • ipa::verify
    • polynomial::compute_g
    • transcript::initialize
    • transcript::reset
    • transcript::hash