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

[debrouxl]

6 commits pushed to the master branch this morning, after more testing I couldn't finish yesterday evening.
* 4 cleanups / improvements split aside from the big emulator support patch;
* support for sending multiple keypresses in a single operation. "122 123,124 125 126,127 128 " is a valid input for the new entry in test_hpcalcs, it posts seven consecutive letters to the calculator;
* logging improvements in test_hpcalcs. I dusted off some older unfinished work I had temporarily set aside.

The master2 branch, with the aforementioned probe and incomplete emulator support, was rebased on master.