D: Add remaining keywords, rdmd in execute command

I added the remaining keywords that weren't present before. See this:
http://dlang.org/lex.html

Additionally, I also added rdmd in execute which enables the developer to execute D program on fly.
I think ```string``` and it's derivatives aren't really library type in D, they are imported automatically similar to python __builtins__ that are imported automatically. I think they need to be highlighted, maybe assigning them to secondary would be the right thing to do?