Adds option to config.pl to force config changes
Adds option to config.pl to force config changes

The script config.pl fails when setting a #define symbol if the symbol isn't
already in the configuration header. This adds an option '--force' to append
the symbol to the end of the file if it isn't already present.

Also clarified usage, and added copyright to the config.pl.

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