v4.0.0

• NEW BEHAVIOR: Setting the viewport rotation now animates by default (pass true for the new immediately parameter to disable) (#2136 @jonasengelmann)
• NEW BEHAVIOR: The auto resize now takes both width and height into account when scaling the contents proportionally to the viewer (#2256 @pearcetm)
• DEPRECATION: Don't access the viewport's degrees property directly anymore; instead use setRotation and getRotation (#2136 @jonasengelmann)
• New gesture: Double-click and drag to zoom (on by default for touch) (#2225 @HamzaTatheer)
• You can now provide a pivot point when rotating the viewport (#2233 #2253 @pearcetm)
• Improved the constraints that keep the image in the viewer, specifically when zoomed out a lot (#2160 @joedf, #2246 @pearcetm)
• You can now provide an element for the navigator (as an alternative to an ID) (#1303 @cameronbaney, #2166 #2175 @joedf)
• Now supporting IIIF "id" and "identifier" in addition to "@id" (#2173 @ahankinson)
• We now delegate tile fetching and caching to the TileSource, to allow for custom tile formats (#2148 @Aiosa)
• Added support for dynamic URLs from tile sources (#2247 @JohnReagan)
• The viewer now emits before-destroy and destroy events (#2239 @pearcetm)
• Auto resize detection is now more efficient (#2256 @pearcetm)
• Improved documentation (#2211 @shyamkumaryadav)
• Fixed: Cropping tiled images with polygons was broken (#2183 @altert)
• Fixed: Boundary constraints were wrong when the viewport was rotated (#2249 @pearcetm)
• Fixed: IIIF tile sizes would be calculated wrong on rare occasions (#2206 @filak)
• Fixed: Disabling buttons only changed their appearance, but they were still clickable (#2187 @pearcetm)
• Fixed: ImageTileSource produced an error having to do with getTileHashKey (#2190 @Aiosa)
• Fixed: On startup you would get an unnecessary "Viewer.buttons is deprecated" warning (#2201 @joedf, #2219 @jssullivan, #2212 @joedf)