Shared Library Changes for Release 2.1.3

Shared library libddcutil is backwardly compatible with the one in ddcutil 2.0.0. The SONAME is unchanged as The released library file is

There is one change of significance. Release 2.1.3 fixes a bug in libddcutil that caused API calls to fail with status code DDCRC_ARG (invalid argument) when passed an otherwise valid display reference for a display that doesn't support DDC/CI. In particular, this caused ddcui to crash when querying information about such a display.