Allow for object oriented c bindings

[jhlange]

This change allows users to create an object oriented binding, by giving a pointer type hint of 'inst' (e.g. the 'instance object' which the given method is using).

As an example, if you were to take the vorbis binding and set the pointer hints to inst instead of ref:

      - {target: ^vorbis_, tips: [inst,ref,ref]}
      - {target: ^ogg_, self: arr, tips: [inst,ref]}

and add this to the rules section:

    function:
      - {action: replace, from: "^_comment_", to: _}
      - {action: replace, from: "^Ogg_stream" }
      - {action: replace, from: "^Ogg_sync" }

The bindings will be object oriented. As an example,

func CommentAddTag(vc *Comment, tag string, contents string) {...}

Becomes:

func (vc *Comment) AddTag(tag string, contents string) {...}

[xlab]

Wow! Thank you for this addition, definitely a good helper.

P.s. although I avoided that feature for long time, because it's very tricky in general case.. But for simple bindings it's great.