Add support for net8.0. Drop support for coreapp3.1

Author: dmiller

Clojure/Clojure.Main/Clojure.Main.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>netcoreapp3.1;net6.0;net7.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
     <StartupObject>Clojure.CljMain</StartupObject>
 	 <PackAsTool>true</PackAsTool>
   </PropertyGroup>

Clojure/build.proj

@@ -26,7 +26,7 @@
 
 	<TestTargetFramework Condition=" '$(TestTargetFramework)' == '' ">net6.0</TestTargetFramework>
 
-	<Error Condition=" '$(TestTargetFramework)' != 'net462' AND '$(TestTargetFramework)' != 'netcoreapp3.1' AND '$(TestTargetFramework)' != 'net7.0' AND '$(TestTargetFramework)' != 'net6.0'"/>
+	<Error Condition=" '$(TestTargetFramework)' != 'net462' AND '$(TestTargetFramework)' != 'net8.0' AND '$(TestTargetFramework)' != 'net7.0' AND '$(TestTargetFramework)' != 'net6.0'"/>
 
 
 	<TestLibraryFramework Condition=" '$(TestTargetFramework)' == 'net462' ">netstandard2.0</TestLibraryFramework>

docs/Preparing-a-release.md

@@ -7,7 +7,7 @@
 * Modify `Clojure\Clojure\Bootstrap\version.properties` to desired release version.
 * Set the version info in `Clojure\CurrentVersion.props`.
     * Please note that you should use lowercase letters only in the pre-release designation in order to avoid problems on non-Windows systems, i.e., `beta1` instead of `Beta1`, `rc1` instead of `RC1`.
-* Build and test.  From the `Clojure` directory with X in {net462, netcoreapp3.1, net6.0, net7.0} (Configuration will default to Debug. Substitute in names accordingly if that is case.)
+* Build and test.  From the `Clojure` directory with X in {net462, net6.0, net7.0, net8.0} (Configuration will default to Debug. Substitute in names accordingly if that is case.)
     * `msbuild build.proj -t:Test -p:TestTargetFramework=X -p:Configuration=Release`
     * `msbuild build.proj -t:TestGen -p:TestTargetFramework=X -p:Configuration=Release`
 * Package.  From the `Clojure` directory, run
@@ -20,7 +20,7 @@
     * clojure-clr-1.10.0-alpha1-Release-net6.0.zip
     * clojure-clr-1.10.0-alpha1-Release-net4.6.1.zip
 * Validate these by any manner of your choosing.  I moved the zips somewhere, unzipped them, and checked that the following start up:
-    * in core3.1, net5.0, and net6.0:
+    * in net6.0 and later:
         * > `Clojure.Main.exe`          (This might not be created on non-Windows builds.)
         * > `dotnet Clojure.Main.dll`
     * in net462: