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.
> we could probably add a D stdlib tags file if that makes sense

Probably best to upload to http://download.geany.org/contrib/tags/ instead - I expect it's a bit big to include in a release for a less-commonly used language.