removed unused and duplicated get-metadata method in AstyanaxReader.
use 4-arg putColumn call in writer
generic `insertMetrics` method should handle string/boolean metrics correctly (like `insertFull`).

I think this is the best approach until the optimizer interfaces can be updated to support `IMetric` instances.

Basically, detect string and boolean by looking for instances of `Metric` and going from there.
keep separate histograms for preaggregated metric sizes

* one for counters, sets and gauges (the single value types)
* one for timers, which deserve special attention.
fix newline goober.