V1.1.10 supports compilation outside Arduino IDE / Linux

fp64lib was primarely targeted to be used as a library in the Arduino IDE. There it works successfully, on both Windows and Linux. However, some users tried to use it outside the Arduino IDE with some success, but also with some errors. As part of a debugging session, I created a small makefile that supports the usual targets “all” and “clean” and creates a library named libfp64.a, which you can then link and use in your projects.