add debug POSTFIX d

[GarrickLin]

I found that I cannot use release version of caffe.dll and caffe.lib when I try to debug my project. It is a good idea to set postfix d to distinguish them just like opencv does.

set(CMAKE_DEBUG_POSTFIX "d" CACHE STRING "Set debug library postfix")

[luoyetx]

@GarrickLin would you like to send a pr?

[luoyetx]

@GarrickLin you can link caffe.lib (release version) for both debug and release in your project. Thus, you need to compile release version first.

[GarrickLin]

I can link caffe.lib successfully but cause an error (something like caffe parser errors) during runtime.