Added instrumented benchmarks.

A new benchmarks/ directory contains versions of the examples that have been instrumented to use controller.da. This provides for uniform timing of wall-time and process-time, reported via stdout.

The controller and instrumented tests are also an example for using libraries/imports and subclasses in DistAlgo code.
Modified benchmarks/controller to use decorator in place of begin/end calls.
Added documentation for controller.da.