Extend cert_write example program by multiple cmd line options
Extend cert_write example program by multiple cmd line options

This commit adds the following command line options to programs/x509/cert_write:
- version (val 1, 2, 3): Set the certificate's version (v1, v2, v3)
- authority_identifier (val 0, 1): Enable or disable the addition of the
                                   authority identifier extension.
- subject_identifier (val 0, 1): Enable or disable the addition of the
                                 subject identifier extension.
- basic_constraints (val 0, 1): Enable or disable the addition of the
                                basic constraints extension.
- md (val MD5, SHA1, SHA256, SHA512): Set the hash function used
                                      when creating the CRT.

NXPmicro/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls