Added support for xUnit-style reporting
Added support for skip reason

Outputs skip reason in NUnit & xUnit xml reports
Merge pull request #36 from JonasSamuelsson/master

Added support for xUnit-style xml reporting, and Skip reasons.
Fix build by making XUnitXmlReportTests pass even when the Fixie version number contains multiple-digit parts.
Update README to include Fluent Assertions in the list of third-party assertion libraries.
Drop support for broken --fixie:listener argument.  It had been added as an early attempt to support XML report output, but has since been obsoleted by AssemblyResult.
Outputs total execution time and total test counts at the bottom of the console output.
Console output includes per-test-assembly duration totals, like TestDriven.NET.
Simplify final summary line output by the console runner.
xUnit xml reporting correctly uses an <assemblies> tag to contain the results of multiple test assemblies.
Simplify implementations of XUnitXmlReport and NUnitXmlReport to take advantage of shorthand provided by the .NET framework's XML classes.
Both NUnit and XUnit style reporting is tested under similar conditions: passes, failures, parameterized tests, and skips with/without skip reasons.
The README describes CI reporting options.
Move ConsoleExtensions.WriteCompoundStackTrace to the one place it is ever called from.
Listener.CaseSkipped(...) accepts a SkipResult containing the Case and optional Reason text, instead of simply the Case.
Added test coverage for skipped test conventions with and without optional reason text providers.
Separate test coverage for the two overloads of CaseBehaviorBuilder.Skip(...).  Rephrased CaseBehaviorBuilder's treatment of the default SkipReasonProvider for readability.
Improves naming of self-tests.
Update README to describe skip reason providers.
Remove duplicated code from StubListener.