Some tweaks to get things happy in Mac-land

I've fixed (I think) the tabs issues I introduced in earlier commits.

Recently added a `Rakefile` to give some quick access to build/tests tasks.

When I run `rake test` on my mac (with this fork) I get a successful build and the following NUnit summary

    Tests run: 54, Failures: 50, Not run: 0, Time: 0.226 seconds

It appears that most-if not all of the tests fail with the following error

    7) ParserTests.AstTests.CommandInvocationOperatorTest : System.TypeLoadException : A type load exception has occurred.
    at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
    at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0

Let's iterate on this PR and hopefully get some/if not all of these changes in before you march too far ahead of me :tongue: