Add Fixture, representing an instance of a test fixture class, to cut down on exessive multiple-arg delegates.
Fixture includes the list of Case objects to be executed together.
Fixture contains the MethodBehavior to use when executing each Case method.
Remove unused arguments.
Rename Convention.Fixtures to Convention.Classes.
Rename Type variables 'fixtureClass' to 'testClass'.
Rename Convention.FixtureExecution to Convention.ClassExecution.
Rename namespace Fixie.Tests.ClassFixtures to Fixie.Tests.TestClasses.
Rename CreateInstancePerFixture to CreateInstancePerTestsClass.
For the SelfTestConvention, rename all sample test classes from *Fixture to *TestClass.
Fixture -> TestClass renaming in LifecycleHookTests.
Test case renaming of Fixture to TestClass.
Rename Fixture.Type to Fixture.TestClass.
Convention class constructors may optionally accept a parameter of type RunContext, which describes how the test run was initiated.  Added 'Explicit' sample convention demonstrating the use of RunContext to mimic NUnit's [Explicit] attribute.
The CommandLineParser parses Main(...)'s incoming args array into a list of test assembly paths and a dictionary of custom key/value pairs.
CommandLineParser exposes a read-only dictionary-like public interface for custom option lookup, and can accumulate multiple values for each key.
CommandLineParser gives instructive error messages whenever the convenience indexer is misused.
Simplify CommandLineParser by having it produce an ILookup<string, string> of the collected custom options.
Fix error messages produced by CommandLineParser.
The RunContext includes custom options parsed from command line arguments.