Add YARP_INT32_FMT and YARP_INT64_FMT defines

These should be used when printing YARP_INT32 and YARP_INT64 variables
instead of %d, %ld, %lld to avoid warnings, for example:

   YARP_INT32 x = 32;
   YARP_INT64 y = 64;
   printf("x = %"YARP_INT32_FMT", y = %"YARP_INT64_FMT, x, y);
Fix -Wformat warning
Include diff_match_patch directory as "SYSTEM"

This option passes the -isystem option to the compiler that avoids
printing warning for these included directories.

We might want to do this for the other external libraries in the future.
Fix -Wunused warnings
Fix Wunused-variable warning
[thrift] match spec for oneway behavior, see #323
Implementing portmonitor dll loader
portmonitor dll plugin loader is implemented and tested. examples and README files are updated.
fixing double free bug on unloading dll by portmonitor
simplifying dll implementaion
updating documentation of the portmonitor to cover the implementation of plugins in dll