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 don't think library aliases like `string` should be in the list of keywords. We should only use language keywords: http://dlang.org/lex.html#Keyword