fix callback issue

[thechampagne]

fix #3

[gitgit3]

I'm not super familiar with github to be honest. How to I pull your bugfix/callback-issue to try it out?
Edit:
It's OK, I figured it out. Just checking it out now.

[gitgit3]

I would have said that the bug is actually in webview c-code, but you've used the arg-pointer to resolve the actual function call. I like it.
Just tested it and it works.

[gitgit3]

I created the pointer to CallbackContext!(BindCallback)* ctx on the heap since I could not figure out a syntax to place it as a static, this may or may not be possible, I am a beginner with D. Maybe you might suggest something. This tripped me up later when I found out that my pointer was being GCd causing a segfault. I stuck the pointers in an array in the class. How did you envisage calling the bind method?