Changes
   * config.h has been split into build_info.h and mbedtls_config.h
     build_info.h is intended to be included from C code directly, while
     mbedtls_config.h is intended to be edited by end users wishing to
     change the build configuration, and should generally only be included from
     build_info.h.
   * The handling of MBEDTLS_CONFIG_FILE has been moved into build_info.h.
   * Config file symbols MBEDTLS_CONFIG_VERSION and MBEDTLS_USER_CONFIG_VERSION
     were introduced for use in MBEDTLS_CONFIG_FILE and
     MBEDTLS_USER_CONFIG_FILE respectively.
     Defining them to a particular value will ensure that mbedtls interprets
     the config file in a way that's compatible with the config file format
     indicated by the value.
     The config file versions are based on the value of MBEDTLS_VERSION_NUMBER
     of the mbedtls version that first introduced that config file format.
     The only value currently supported is 0x03000000.