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

[danielmewes]

I've fixed a couple of bugs in the protocol implementation.
You can find my fixes here https://github.com/danielmewes/hplp/
I've also submitted a pull request to debrouxl https://github.com/debrouxl/hplp/pull/2 , so the changes will hopefully find their way into the main repo eventually.

I can now backup my Prime (latest firmware 6975) on Linux and also send apps back to the calculator without any apparent corruption (tested with an app of 1.8 KB).
Thank you so much for this awesome software @debrouxl!

Screenshots work as well, though type 8 doesn't work for me. Type 9 gives the best results, even though the colors are somewhat off.