Cleanup: remove old VS solution, update README

- Remove Builds/MsVc2022.win/ (old MSBuild solution, superseded by CMake)
- Update README.md: replace v3.0 header/intro with current description,
  replace old Downloads section (InnoSetup zip + MSBuild badge) with
  GitHub Releases link, fix VS build instructions to use CMake-generated
  solution instead of deleted Builds/MsVc2022.win/OdbcFb.sln
- Update tests/README.md: replace MsVc2022.win build reference with
  Invoke-Build install instruction
- Clean up stale Install/Win32/install_image/ entry from .gitignore

Author: fdcastel

.gitignore

@@ -3,7 +3,6 @@ Builds/*/x64/
 Builds/*/ARM/
 Builds/*/ARM64/
 Builds/*/.vs/
-Install/Win32/install_image/
 *.suo
 *.ncb
 *.user