added a - almost clean - include #{str_tmpl} feature :D

Hello,
I added a functions to vibe/templ/diet.d to inject a compile-time generated diet-template into an exsiting template
the code should be fairly obivous. 
Could you review it ?
In return I'll add alot of documentation to vibe.d :D
rationals at
http://forum.rejectedsoftware.com/groups/rejectedsoftware.vibed/thread/10332/
update!
you can now say
enum hello = "h1 Hello World"
stringIncludeRender!("templ.dt",hello)

If the templ.dt looks like this
html
  head 
    title Hello World
  body 
    include #{hello}

you should see Hello World :D