add cpp-lib example; some fixes

cpp-lib/readme.md

@@ -0,0 +1,39 @@
+
+Build
+-----
+
+Switch to `cpp/` and do:
+```
+qmake lib.pro
+make
+```
+
+
+Run
+---
+
+```
+$ lqml ~/slime/qml-start-swank.lisp
+$ emacs
+```
+
+In Slime do:
+```
+(defvar *cpp* (qload-c++ "cpp"))
+
+(define-qt-wrappers *cpp*)
+
+(hello *cpp* '(1 "two" (1.25 #(50 -50 75))))
+```
+Now look at the console output where you launched the `lqml` executable.
+
+As you can see, although the argument and return type are simply defined as
+`QVariant`, you may also pass lists, because a `QVariant` can also be of type
+`QVariantList`, so this is a perfect fit for (nested) Lisp lists.
+
+So, we pass a nested Lisp list, and it gets printed on Qt side with the
+respective types. Then the `QVariantList` is returend to Lisp, where it is
+automatically converted back to a nested Lisp list.
+
+Realy convenient!
+