Reference Viewer v0.5 update

I was working on another extension when I noticed the Reference Viewer was not working anymore. The problem was that the other extension redefined a function that was used by the Reference Viewer and, as a result, it stopped working. This issue, when one extension conflicts with another, can be avoided using local functions instead of global functions.

This update is mainly to fix this, but there are also some other minor changes.

Changes/Fixes

• Using local functions instead of global ones to avoid possible conflicts with other extensions/plugins.
• Fixed issue that caused the image to be 'nil' when canvas size was 0.
• Show version number in the window title.

*Edit:

Showing version number requires Aseprite 1.3.13. A hotfix has been applied (v0.5.1) so it doesn't give an error in older versions.

*Edit2:

Fixed typo in last update (v0.5.2). From "app.version.path" to "app.version.patch". Update v0.5.3 to use app.apiVersion instead of app.version, which works well also if Aseprite is build from source. I hope this is the last edit (sorry for the inconveniences).