Remove usage of float

Applying ron064 idea (https://github.com/pebble-bike/PebbleBike-PebbleWatchFace/issues/8)

Memory usage:
=============
Before
* Total app footprint in RAM:      17130 bytes / ~24kb
* Free RAM available (heap):        7446 bytes

After
* Total app footprint in RAM:      15346 bytes / ~24kb
* Free RAM available (heap):        9230 bytes
Round speed instead of truncate them
set_layer_attr_full instead of set_layer_attr to save more memory

Thanks ron064's idea

Free RAM available (heap): 7954 => 7790  (-164 bytes)
Merge remote-tracking branch 'github_pb/master' into ReduceMem
Merge remote-tracking branch 'github/feature_remove_float'