Improvement: Use librato complex measurements.

For `measure.` and `measure#`  metrics, the follow data is produced:
min, median, p95, p99, max, sum, count, mean, last. Currently, this
data is being submitted to Librato as 9 seperate metrics. This can
become expensive. Librato supports a complex metric type. The complex
metric counts as 1 metric when it comes to billing but includes:
min, max, sum, count, mean. This just leaves median, p95, and p99 to
be submitted out of band. It is also reasonable to expect that librato
will accept quantiles in the medium term future.
Merge pull request #102 from ryandotsmith/complex-measurements

Improvement: Use librato complex measurements.