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.Cli.Tests/Expectations/Help/NoDescription.Output.verified.txt

@@ -0,0 +1,8 @@
+USAGE:
+    myapp [OPTIONS] <COMMAND>
+
+OPTIONS:
+    -h, --help    Prints help information
+
+COMMANDS:
+    bar