[OpenCV2] add library for projects that require the C API

[cenit]

as per title, I propose the inclusion of the older OpenCV 2, guarded with an error like MySQL/MariaDB, since it is necessary to build projects that still use the C API (abandoned/broken in OpenCV3). For example, it is necessary to build YOLO on Windows ;)

[cenit]

I did another commit, to fix building on macOS (I hope it fixes also Ubuntu, still not tested). Since vcpkg is now cross-platform, I hope it is better now 🤓

[cenit]

I tested building also on Ubuntu and it worked. Added a small notice (comment) at the beginning of the port file to explain pre-requisites.

[cenit]

As a side note, I tried building also on x86-windows but I got a failure when linking with OpenGL32.lib, with the linker complaining that it couldn't solve _imp_wglGetProcAddress symbol...

[cenit]

I think that this port is in a good shape to be at least tried by someone, if interested @ras0219-msft @UnaNancyOwen @patrikhuber @jasjuang

[patrikhuber]

@cenit Thanks, it might become useful some day (as you mentioned... YOLO & stuff...), but for now I long moved to OpenCV3 (and probably 4 soon) for my own projects :-)

[jasjuang]

@cenit Thanks but I have move forwarded to OpenCV3 a few years ago for my projects so I won't be able to test it.

[cenit]

closed because there's not enough interest and it would be difficult to keep tested (vcpkg discourages not using the latest version by design)