D Parsing (again)/ D grammar

[Philippe Sigaud via Digitalmars-d]

> Anyway, thank you very much for the code. The weekend is coming -> I'll play
> with your implementation and see if there any improvements possible.

Be sure to keep me informed of any enormous mistake I made. I tried
Appender and other concatenation means, without big success.

Btw, I saw on the ML that using byKeys.front() is very slow. Use
keys[0] of somesuch instead.