Make debug postfix optional

Make debug postfix optional

Library debug postfix might not be suitable for cross platform project, and usually require extra work of link against prebuilt yaml-cpp.

Generally, Xcode project output library to these directories:

    Debug
    Release
    Debug-iphoneos
    Release-iphoneos
    Debug-iphonesimulator
    Release-iphonesimulator
Another Xcode project usually configured its build setting as follow, and expects library name to be same between Release and Debug

    LIBRARY_SEARCH_PATHS=$(CONFIGURATION)$(EFFECT_PLATFORM_NAME)
    OTHER_LDFLAGS= $(inherited) -lentityx