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/NoVersion.Output.verified.txt

@@ -0,0 +1,12 @@
+USAGE:
+    myapp <FOO> <BAR> <BAZ> <CORGI> [QUX] [OPTIONS]
+
+ARGUMENTS:
+    <FOO>
+    <BAR>
+    <BAZ>
+    <CORGI>
+    [QUX]
+
+OPTIONS:
+    -h, --help    Prints help information