Import debugStream library from icub-main with a few small changes

* Rename "ICUB_" environment variables "YARP_".
* Implement deprecated methods in order not to break anything
* Use ACE_OS::vsnprintf instead of vsprintf.
* Do not deprecate yarp_print_trace.
* Implement yarp_print_trace using ACE to make it available on every
  platform.
* Use yarp_print_trace after yAbort().
* Add yAssert macro and deprecate YARP_ASSERT
Replace all occourrences of deprecated YARP_LOG_ERROR with yError
Replace all occourrences of deprecated YARP_LOG_INFO and yarp_show_info+printf with yInfo
Replace all occourrences of deprecated YARP_LOG_DEBUG and yarp_show_debug+printf with yDebug
Replace all occourrences of deprecated yarp_show_warn+printf with yWarning
Replace all occourrences of deprecated YARP_ASSERT with yAssert
Bump tweak version
Merge pull request #252 from drdanz/yDebug

Import debugStream library from icub-main