Remove the last remnants of the old grammar.

[ehuss]

Now that the reference includes the complete grammar, I think the last remaining references to the old grammar can be removed. This includes a few different changes (I can split these up if you'd like):

• Remove some references to the old grammar's rule names.
• Remove the link to the old grammar.
• Fix a bug with the ClosureExpression rule which didn't correctly allow for untyped parameters. Also rewrote some of the closure text when removing the old rule names.
• Remove some of the grammar descriptions that only applied to the old grammar.
• Added a brief description of the notation based on some unfinished work by brauliobz.

[matthewjasper]

This needs a rebase

[ehuss]

Sorry, I keep forgetting that github doesn't alert for conflicts.

[matthewjasper]

Thanks!