Release imv v2.1.3

Release v2.1.2

* Fix compatibility with older gcc versions

* Fix bug where unchanged files were unnecessarily reloaded
* Fix bug where first frame of gif or first slide was changed to quickly
* Minor performance improvements

Release v2.1.0

Release imv v2.0.0

Release version v1.2.0

Release v1.1.0

Release version v1.0.0