Initial groundwork for rsvg bindings

Add scratch files as a start: merge rsvg.h and rsvg-cairo.h.
Concatenate licenses of rsvg.h and rsvg-cairo.
Remove unnecessary defines, private structs, unused apis
(GIO/GdkPixbuf), etc.
Replace deprecated api functions with glib-object functions
Add headers for glib.h and librsvg/rsvg.h
Replace glib types with primitive types

This help tolua++ to recognize them as native types and not as
usertypes.
Remove unused GIO/GdkPixbuf interface

Conky Lua only uses cairo, so that's everything we need to keep.
Anything else is just a source for trouble.
Inline typedefs
Wrapper functions for {creat,destroy}ing an rsvg handle

This wrapper functions should facilitate the handling of rsvg handles.
Especially unrefing with g_object_unref does not seem to work properly
using the lua bindings.
Functions for creating and accessing Dimension/Position structs
Include header file for helper functions

Also add function declarations
Add rsvg bindings to cmake build framework
Merge pull request #13 from jrk-/rsvg

Lua bindings to librsvg