Big changes:

Converted from Add-on to Extension. It allowed me to bundle the addon dependencies with it.
Now you need to drag-and-drop the extension .zip archive into blender to install it
Added new UI panels to perform common operations quickly and to edit custom data used by the game
Implemented a rename detection system to keep property names and action data paths updated. You can disable automatic action updates in the addon tools panel
Implemented camera import and export. Now you can adjust the Army Painter camera for the model
Added automatic sga extraction. Now you don't need to unpack textures manually

Other improvements

The addon now remembers the options of the last export and import so you don't need to set it up every time
Configured a custom shape for markers to make them look consistent with Object Editor #8
Added automatic bone weight normalization
Exported textures are now compatible with Object Editor
Added drag-and-drop support. Now you can simply drop your .whm file into blender.
Supported parenting a mesh to a single bone #10
Vertex merging is now configurable in the export dialogue.
Read this for a small guide on these parameters.
You may want to reexport old models with Vertex merging position threshold = 0.01 to reduce the vertex count
Implemented parsing of tga data in rsh textures
Added a few new warnings for possible errors #4
Made asserts optional and added a "Strict mode" with the old behavior
Added better property descriptions

Fixed incorrect marker orientation in blender.
If you are working on a model imported by an old version use the "Legacy markers" option in the export dialogue.
Fixed material requiring full_path property
Finally removed Dots Stroke material
Pinned quicktex version to 0.2.1 #4
Added support for meshes with [ in the name
Fixed incorrect vertex normal export #3 #5
Added hashing of long object names when used as a part of a property name
Fixed mesh properties being case-sensitive #6
Fixed export of internal textures #9
Fixed random animation corruption in export #11
Removed wield modifiers because it breaks banners #12
Fixed vertex merging #14
Added correct import and export for animations with fps not equal to 30 #16