CONTRIB: move spoa_example out of the tree

As previously mentioned SPOA code has nothing to do in the haproxy core
since they're not dependent on haproxy's version. This one was moved to
its own repository here with complete history:

     https://github.com/haproxy/spoa-example
diff --git a/doc/SPOE.txt b/doc/SPOE.txt
index 71c7fde..2ed7878 100644
--- a/doc/SPOE.txt
+++ b/doc/SPOE.txt
@@ -77,6 +77,10 @@
 spite of these limited features, we can easily imagine to implement SSO
 solution, ip reputation or ip geolocation services.
 
+Some example implementations in various languages are linked to from the
+HAProxy Wiki page dedicated to this mechanism:
+
+ https://github.com/haproxy/wiki/wiki/SPOE:-Stream-Processing-Offloading-Engine
 
 2. SPOE configuration
 ----------------------