Direct execution of agents

[CharliePoole]

Allow execution of agents from the command-line with a simplified set of options and the path to a single test assembly file,

Output similar to the console runner will be produced and no options not already defined by our agents will be added. Executing in this way will run all tests in the specified assembly, displaying the results.

The primary purpose of this change is to allow easy testing of our pluggable agents. A secondary use may be found in debugging issues presented by users, where the console runner does not display sufficient information.