libhpcalcs: portable (Windows / MacOS X / Linux) connectivity kit library

[debrouxl]

Looks like the entire program (or so) gets transferred, but nothing clearly wrong occurred.

As for screenshots, I forgot to mention that only formats 8 to 11 will yield a non-unusable (*) result. I've just edited the message in test_hpcalcs.c, the change will be in the next commit.

*: inverted colors in 4 bpp mode, and a grayscale image in 16 bpp mode. I know what post-processing needs to be done, but I haven't implemented it yet.

EDIT: I have pushed a commit with multiple fixes, the improved README, and an indication of the (most) valid screenshot formats