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/Leaf.Output.verified.txt

@@ -0,0 +1,15 @@
+DESCRIPTION:
+The lion command.
+
+USAGE:
+    myapp cat [LEGS] lion <TEETH> [OPTIONS]
+
+ARGUMENTS:
+    <TEETH>    The number of teeth the lion has
+
+OPTIONS:
+                             DEFAULT
+    -h, --help                                   Prints help information
+    -c <CHILDREN>                                The number of children the lion has
+    -d <DAY>                 Monday, Thursday    The days the lion goes hunting
+    -w, --weight [WEIGHT]                        The weight of the lion, in kgs