Set version to 2.8.3 (semver 28.3)

The previous version number choice, 2.8.2.1, was a mistake, as there
were several changes, not just bug fixes

Core/AssemblyVersion.cs

@@ -14,5 +14,5 @@
 // command to change the version number which, I guess, produces an incompatible 
 // assembly in the presence of strong names (strong naming prevents two assemblies 
 // from linking together without an exact match.)
-[assembly: AssemblyVersion("2.8.2.1")]
-[assembly: AssemblyFileVersion("2.8.2.1")]
+[assembly: AssemblyVersion("2.8.3")]
+[assembly: AssemblyFileVersion("2.8.3")]

appveyor.yml

@@ -1,4 +1,4 @@
-version: 2.8.2.{build}
+version: 2.8.3.{build}
 
 # Try to fix "The project file ... is not supported by MSBuild and cannot be built."
 image: Visual Studio 2019
@@ -14,7 +14,7 @@ before_build:
 build_script:
     # First, set some environment variables.
     # SEMVER is set manually. Not sure how this can be automated.
-    - set SEMVER=28.2.1
+    - set SEMVER=28.3.0
     - echo %APPVEYOR_REPO_TAG%
     # Build packages as SEMVER-ci{build}
     - ps: if ($env:APPVEYOR_REPO_TAG -eq $True) { $env:PKG_VERSION = $env:SEMVER; } else { $env:PKG_VERSION = "$($env:SEMVER)-ci$($env:APPVEYOR_BUILD_NUMBER)"; }