Release 3.4.3

Changes

• Fixed bug in .NET serialization code where an incorrect number of bytes was written when using
  ZLIB compression.
• Fixed an issue with .NET functions Encryptor.EncryptSymmetric..., where asymmetric encryption
  was done instead of symmetric encryption.
• Prevented KeyGenerator::galois_keys and KeyGenerator::relin_keys from being called when the
  encryption parameters do not support keyswitching.
• Fixed a bug in Decryptor::invariant_noise_budget where the computed noise budget was
  log(plain_modulus) bits smaller than it was supposed to be.
• Removed support for Microsoft GSL gsl::multi_span, as it was recently deprecated in GSL.