prebuilt opencv is no longer compatible with emscripten

[pjbaron]

Emscripten has changed the fundamental data size of the "size_t" structure, attempting to rebuild main.cpp with the current emscripten will trigger a series of undefined reference errors from the prebuilt opencv library files, including _Znaj which is mentioned here and here

Thanks for making this public, it's great to see working examples of emscripten with opencv they are fairly rare (there are a lot of broken ones though)

Perhaps you could update the readme with the versions of emscripten, node and opencv you used so we can play around without the opencv rebuild? I understand that writing up how to build opencv with emscripten is a big job (I've just spent half a day trying)