Update the documentation to indicated which module each class is
located. This allows the documentation to be referenced from other
modules as well as enabling links to the source code directly from the
documentation.
- Add process_raw() method to the API. This is inteneded to be invoked
on any raw output (i.e. not MeasurmentCsv) generated by an Instrument.
- Both process() process_raw() are portional to be overriden by
impolementation; the default behavior is to return an empty list.
- The output specification for both is extened to allow
MeasurementCsv's, as well as DerivedMetric's.
- Documentation has been reworded for clarity.
DerivedMeasurments processors now return DerviedMetrics rather than
measurments. The notion of an InstrumentChannel doesn't really make
sense in the context of DerivedMeasurments, which are not directly
measured on the target. Since Measurement's require a channel, a simpler
DerviedMetric is added that only requires a name and a type.
