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.
Derived metrics may be calculated form data in raw output that is not
present in the resulting MeasurementCSV. This adds a method to provide
uniform access to raw artifacts generated by an instrument.
- Fix missing parameter in the documentation
- Clarify meaning of `sites` and `kinds` in the documentation.
- With the current implementation the `channels` argument is
useless: if `sites` and `kinds` are not also specified then all
channels are enabled anyway. Fix that by making those parameters
ignored when `channels` is provided.
Perviously, a parameter passed into SshConnection controlled whether the
connection was established over SSH or Telnet. Now, there is a separate
class for Telnet connections.
