Next step following various suggestions

Following @Scottmitch review
1) Use System.nanoTime() instead of System.currentTimeMillis()

2) Minimize call to System.nanoTime()

3) Use StringBuilder when possible

4) Remove / 10 ° 10 since no more sleep usage

5) Minimize locked part in GlobalTraffic to the minimal a little more

6) Use nanoTime instead of currentTime such that time spend is computed,
not real time clock. Therefore the "now" relative time (nanoTime based)
is passed on all sub methods.

7) Take care of removal of the handler to force write all pending writes
and release read too

8) Review Javadoc to explicit:
- recommandations to take into account isWritable
- recommandations to provide reasonable message size according to
traffic shaping limit
- explicit "best effort" traffic shaping behavior when changing
configuration dynamically