Add (optional) Google Protocol Buffers support (example in Tutorial 3).

To use protobuf, run cmake as follows:
cmake -DUSE_PROTOBUF=1 ..
For this, protobuf library has to be installed on the system.

Further changes:
Clean up splitter/merger: default are N-to-1-merger and 1-to-N-splitter.
Fix bug in nanomsg message deallocation.
Setup proper buffer sizes for nanomsg/zeromq via cmake/bash script.
chmod +x for start scripts.

fairmq/prototest/payload.proto

@@ -0,0 +1,13 @@
+package sampler;
+
+message Content {
+    optional double a = 1;
+    optional double b = 2;
+    optional int32 x = 3;
+    optional int32 y = 4;
+    optional int32 z = 5;
+}
+
+message Payload {
+    repeated Content data = 1;
+}