Added a builder for ConsoleReporter.

Closes #361.
Added a builder for CsvReporter.

Closes #362.
Added a builder for JmxReporter.
Added a builder for Slf4jReporter.

Closes #363.
Make the directory required for CsvReporter.
Added a builder for GangliaReporter.

Closes #365.
Added a builder for GraphiteReporter.

Closes #366.
Update docs for metrics-ganglia.
Update docs for metrics-graphite.
Added docs for the core reporters.
Added Timers backed with arbitrary Samples.
Drop SampleType.

Just accept Sample instances.
Added TimeSlidingWindowSample.
Standardize on "sliding window".

So, SlidingWindowSample and SlidingTimeWindowSample.
Drop Sample#clear().
Updates docs for the sliding window samples.
Ditch the factory methods for ExponentiallyDecayingSample and UniformSample.

Easier here to just use constructors.
Drop TODO.md.

All of these are tickets, basically.
Added Caliper benchmarks for Sample types.
Added benchmarks for counters and meters.