Default behavior changes
   * Some default policies for X.509 certificate verification and TLS have
     changed: curves and hashes weaker than 255 bits are no longer accepted
     by default. The default order in TLS now favors faster curves over larger
     curves.

Removals
   * Remove the compile-time option
     MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE.