Superstructure - Windows snapshot build 81ccfe3f

An early prototype of Superstructure, a structural FE tool.
Run frontend.exe to start with an empty workspace, or open a
saved model with: frontend.exe path\to\model.ssm

Requirements:
- 64-bit Windows 10 or later, with a Vulkan-capable GPU and
  current graphics drivers
- Microsoft Visual C++ Redistributable (x64):
  https://aka.ms/vs/17/release/vc_redist.x64.exe

Third-party licences:
The licenses folder contains the licence text for every bundled
library. NGSolve and Netgen are LGPL-licensed and dynamically
linked; our builds carry local modifications, and the
corresponding source is available on request
(til@superstructur.es). Upstream: https://github.com/NGSolve/ngsolve

