Release 1.0.0a3

(1) fix issue #24 (for good this time);
(2) add support for two new verification models for SMPTE-TT (st2052-2010, st2052-2013);
(3) add --external-schema option;
(4) add --show-validator option;

ttv-1.0.0a2

Fix issues #20, #23, and #24.

ttv-1.0.0a1

Initial alpha release.