Swap out fingerprinting infrastructure.

All old database entries should be deleted.  :-(
The Prometheus Go client has a new handler API.
MetricPersistence.AppendSample signature changes.

``MetricPersistence.AppendSample(*model.Sample)`` -> ``MetricPersistence.AppendSample(model.Sample)``.
Simplifications of GetFingerprintsForLabelSet.

``MetricPersistence.GetFingerprintsForLabelSet(s *model.LabelSet)`` ->
``MetricPersistence.GetFingerprintsForLabelSet(s model.LabelSet)``.
GetFingerprintsForLabelName simplifications.

``MetricPersistence.GetFingerprintsForLabelName(l *model.LabelName)``
->
``MetricPersistence.GetFingerprintsForLabelName(l model.LabelName)``
Interface simplifications: GetValueAtTime().

Pointer arguments to copies.
Interface simplifications.

GetBoundaryValues() from pointers to values.
Interface simplifications: GetRangeValues

From pointers to copies.
Interface simplifications.

GetFingerprintsForLabelSet ([]*Fingerprint, error) ->
GetFingerprintsForLabelSet ([]Fingerprint, error)
Interface simplifications.

GetFingerprintsForLabelName ([]*Fingerprint, error) ->
GetFingerprintsForLabelName ([]Fingerprint, error)
Interface simplification.

GetMetricForFingerprint(model.Fingerprint) (*Metric, error) ->
GetMetricForFingerprint(model.Fingerprint) (Metric, error)
Checkpoint for Julius.

DONOTMERGE - Buggy in-memory implementation.

MOST BUT NOT ALL TESTS PASS.  NAIVE IMPLEMENTATION: 6-20x performance
improvement for existing workflow.

There is no layercake.

The basic tests for the MetricPersistence have been extracted and re-applied
to both LevelDB and Skip List.