Add rx-merge-delay-error operator (#417)

* Add rx-merge-delay-error operator

* fix of msvc2013 compilation

* fix #417 comments

Added RXCPP_NOEXCEPT macro; Added doxygen scenarios for composite_exception and merge_delay_error; Fixed composing exception in merge_delay_error operator; Modified test for merge_delay_operator

* #417 fix composite_exception example

* #417 fix merge_delay_error doxygen example

* fix: samples add among others in project doxygen CMakeLists.txt

* fix: composite_exception.cpp example