Rename ZooKeeperTraceFilter to ZooKeeperSamplingTraceFilter.
Add README.md for brave-tracefilters.
Add LICENSE file in all sub modules.
Add FixedSampleRateTraceFilter and tests.
Remove TraceAllTraceFilter as it became obsolete with the introduction of FixedSampleRateTraceFilter.
Update brave-tracefilters documentation.
Clean-up unused constants in test classes.