added 'include' helper for #182

I added an "include" helper to allow passing of distinct objects down to the partial. Mainly inspired by @chickenwing and @ustun.
I did so after investigating into the structure of the compiler because I didn't see any obvious solution to reference the correct context (mainly due to missing knowledge about bison compilers in general).

Caveat: The helper only finds partials that are correctly registered and not passed in through compile options.