[timers] make systick_isr atomic to avoid cm_time_sec & cm_time_msec mismatches
[timers] add u64 & s64 types (to be used for timer code)
[main] sanity check on type sized (could be converted to compile asserts later on)
[js] support boolean operations on FP numbers
[js] add obj_set_property_fp utility function
[timers] have event timestamps in usec resolution