Prepare for a separate major version of CloudNative.CloudEvents.Mqtt

This more fine-grained way of referring to the versions will allow us to still only change Directory.Build.props just before a release, but have separate major versions flow from that.

RELEASING.md

@@ -43,13 +43,20 @@ Within this repository, this is achieved by the following mechanisms:
 
 - Individual csproj files do not specify a version
 - The [Directory.Build.props](src/Directory.Build.props) file has a `<Version>` element
-  specifying the version of all packages
+  specifying the version of all packages which don't need a separate major
 
 A single GitHub release (and tag) will be created for each beta release, to cover all packages.
 
 - Example tag name: "CloudNative.CloudEvents.All-2.0.0"
 - Example release title: "All packages version 2.0.0"
 
+### Exception: new major versions
+
+Sometimes, we need a new major version of a "satellite" package, typically
+to adopt a new major version of a dependency. In this case, the satellite package
+will have its own major version, but keep the minor and patch version of everything
+else.
+
 ## New / unstable package versioning
 
 New packages are introduced with alpha and beta versions as would

src/Directory.Build.props

@@ -1,11 +1,22 @@
 <Project>
   <PropertyGroup>
     <!-- 
-      - We use the same version number for all stable
-      - packages. See RELEASING.md for details.
+      - We use the same minor/patch version number for all stable
+      - packages, and the same major for most packages.
+      - See RELEASING.md for details.
       -->
-    <Version>2.7.1</Version>
-    <PackageValidationBaselineVersion>2.7.0</PackageValidationBaselineVersion>
+    <MajorVersion>2</MajorVersion>
+    <MinorVersion>7</MinorVersion>
+    <PatchVersion>1</PatchVersion>
+    <PackageValidationMinor>7</PackageValidationMinor>
+    <Version>$(MajorVersion).$(MinorVersion).$(PatchVersion)</Version>
+    <!-- 
+      - The version used for detecting breaking changes.
+      - This is always older than the current version (except when creating a new major)
+      - and is the patch-0 of either the current minor (if the current patch is non-zero)
+      - or the previous minor (if the current patch is zero).
+      -->
+    <PackageValidationBaselineVersion>2.$(PackageValidationMinor).0</PackageValidationBaselineVersion>
     
     <!-- Make the repository root available for other properties -->
     <RepoRoot>$([System.IO.Path]::GetDirectoryName($([MSBuild]::GetPathOfFileAbove('.gitignore', '$(MSBuildThisFileDirectory)'))))</RepoRoot>