Updated things. Added basic parsing.

Changed IGrammar to an abstract class as need to use properties, which
you can't do with interfaces.
Changed from auto-properties, as I don't like having public variables
with { private get; }. Anything that has public get/set is still auto
property.
There's now basic parsing from the console. There's no validation or
anything right now really, I'll add that later.
You can create methods and add them to specific grammar objects, which
can then be executed.
Added a Sentence object, contains a list of grammar objects that makes
up a sentence.