gdk3: add a missing space after ","
gdk3: use types provided by GLib

 int ->
gint
^
gdk3: remove too much space
gdk3: remove needless nil check

RVAL2GDKCURSOR() (RVAL2GBOXED()) returns NULL for nil.
gdk3: use meaningful name
gdk3: add a missing space after ","
gdk3: fold a long line
gstreamer: support GstValueList conversion
gstreamer: Gst::Structure#fields return value instead of GValue itself

Because value has type information. So we don't need to pass GValue to
user directly. (GValue has GType and value itself.)
gstreamer gst-inspect: support showing cap info
glib2: add GValue#to_s
Revert "gstreamer: Gst::Structure#fields return value instead of GValue itself"

This reverts commit a77226e79ae2985c7532deab071628ac21b6c7b7.

Because now we have an uesful method in GValue, #to_s.
gstreamer: make gst_value_XXX() functions mapping more Ruby-ish

We map gst_value_XXX() functions to Gst::ValueFunctions.#XXX. And we
wrap them as methods like:

   module Gst::ValueMethods
     def XXX
       Gst::ValueFunctions.XXX(self)
     end
   end

Then we extend Gst::ValueMthods for GValue returned by GStreamer. For
example, GValues returned from Gst::Struct#fields.
gstreamer gst-inspect: use GValue#serialize
gstreamer gst-inspect: add an empty line after pad template info
gstreamer gst-inspect: add missing ":" after label
gstreamer gst-inspect: remove needless empty line
gstreamer gst-inspect: support URI handler information
gstreamer gst-inspect: don't show default for object type
goocanvas: update FSF address

GitHub: fixes #201

Reported by ktdreyer. Thanks!!!