Merge remote-tracking branch 'origin/topic/timw/776-using-statements'

* origin/topic/timw/776-using-statements:
  Remove 'using namespace std' from SerialTypes.h
  Remove other using statements from headers
  GH-776: Remove using statements added by PR 770

Includes small fixes in files that changed since the merge request was
made.

Also includes a few small indentation fixes.

src/plugin/Manager.cc

@@ -17,6 +17,7 @@
 #include "../util.h"
 #include "../input.h"
 
+using namespace std;
 using namespace plugin;
 
 Plugin* Manager::current_plugin = nullptr;