Move non-public classes and functions to psync::detail namespace

CompressionScheme, CompressionError, and MissingDataInfo, which are
public types, are instead moved to a new header PSync/common.hpp

Change-Id: If1b8cb037cb321ff32c080c67df9dc3689223c00
diff --git a/tests/test-producer-base.cpp b/tests/test-producer-base.cpp
index 4320e83..8e9dd77 100644
--- a/tests/test-producer-base.cpp
+++ b/tests/test-producer-base.cpp
@@ -18,7 +18,6 @@
  **/
 
 #include "PSync/producer-base.hpp"
-#include "PSync/detail/util.hpp"
 
 #include "tests/boost-test.hpp"
 
@@ -32,7 +31,7 @@
 
 BOOST_AUTO_TEST_SUITE(TestProducerBase)
 
-BOOST_AUTO_TEST_CASE(Ctor)
+BOOST_AUTO_TEST_CASE(Constructor)
 {
   util::DummyClientFace face;
   BOOST_REQUIRE_NO_THROW(ProducerBase(40, face, Name("/psync"), Name("/testUser")));