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.
If you can use `string` as a normal identifier (ie. variable/parameter name), then it shouldn't be highlighted as a keyword IMO, since Geany's highlighting isn't context sensitive. I don't know D at all but I tried this before in C++ and it's quite annoying, kind of like this: <code>std::**string** **string**("hi");</code>