Changed, Classic modes: bigger Thing arrows are now rendered when thing sprite rendering is skipped.
Changed, Classic modes: when "Fixed Things Scale" option is enabled, thing size stays at 2x scale instead of 1x when extra bounding box is rendered.
Added Preferences -> Appearance -> "Things transparency (Things mode)" slider.
Renamed Preferences -> Appearance -> "Things transparency" to "Things transparency (other modes)".
Externalized thing bounding box and arrow texture, used to render things in Classic modes (Textures/ThingTexture2D.png).
Updated ZDoom_DECORATE.cfg (A_SetUserVarFloat, A_SetUserArrayFloat).
DECORATE: added "$obsolete" special comment. When present, it marks the thing as obsolete. It will be detected by "Check obsolete thing" Map Analysis Mode check and will be marked in the Thing Properties Window and the Thing Info panel.
Map Analysis mode: added "Check obsolete things" check.
Updated documentation ("DECORATE keys" page).
Updated ZDoom_DECORATE.cfg.