Fixed issues with static methods.

`Stacktrace::get_frame_context()` assumes that if the method doesn't exist it's available through `__call`. However, if it's a static method it won't find it (and throw a `ReflectionException`). I fixed this by checking if `$frame['type']` is `::` and, if that's the case, it calls `__callStatic` instead.
Merge pull request #73 from jyggen/patch-1

Fixed issues with static methods.