0.5.21: 3D HighDPI, better error handling, smaller installer

0.5.21 is a minor release that drops the demo tabs from the installer, making it ~5 MB smaller. It also adds support for HighDPI 3D rendering, which can be customized via the new graphics.render_scale option. The mesh importer also now has a reload meshes button, which can be handy for editing meshes in Blender while also importing them into a new OpenSim model.

Apart from that, there's a few bugfixes, and the production/development pipeline has been generally updated to accomodate new features, release methods, and so on.

As always, all changes are listed in the CHANGELOG.md file!