Merge pull request #1 from Jentsch/gradient_time_synchronization_protocol

Removed a float in gtsp_compute_rate
fixed code standard compliance and minor issues
Merge branch 'gradient_time_synchronization_protocol' of github.com:phiros/RIOT into gradient_time_synchronization_protocol
Since no part of the offset sum (sum_offset) is below _gtsp_jump_threshold (gtsp.c: 153) the absolute of the average could only be greater than ABS(_gtsp_jump_threshold) if it is positive. With that knowledge the absolute calculation can be safely removed.