Preparations for the 1.0 release

* Less cluttered solution layout.
* Move examples to a repository of its own.
* Move Roslyn analyzer to a repository of its own.
* Enable central package management.
* Clean up csproj files.
* Add README file to NuGet packages.

src/Tests/Spectre.Console.Tests/Expectations/Cli/Help/RootExamples_Leafs.Output.verified.txt

@@ -0,0 +1,13 @@
+USAGE:
+    myapp [OPTIONS] <COMMAND>
+
+EXAMPLES:
+    myapp animal dog --name Rufus --age 12 --good-boy
+    myapp animal horse --name Brutus
+
+OPTIONS:
+    -h, --help       Prints help information
+    -v, --version    Prints version information
+
+COMMANDS:
+    animal    The animal command