Added filtering of ascent speed: In the previous version the ascent speed was simply calculated based of the last measured pressure values. This may lead to unexpected colorchanges of the depth value. To smooth this behavior a filter has been added which evaluates if a movment direction is valid for a certain period of time. If the condition direction is stable then the ascend speed is provided.

Imported from Ac6/SystemWorkbench/plugins/fr.ac6.mcu.firmware_1.14.7.201711101414/resources/builtin/:
* File syscalls.c