TODO

check status more often, at least to check for memory allocation errors
when creating a new object.

Probably should use Lua allocator instead of malloc.

Maybe provide a Lua API for other modules to use from C to create objects
using my metatables but based on existing pointers supplied as light user
data.  Also the reverse: return a light user data containing the actual
pointer from a userdata (or can I just tell people what metatable name to
use and let them dereference it).

These functions aren't bound at all yet:
cairo_copy_clip_rectangle_list
cairo_ft_font_face_create_for_ft_face
cairo_ft_font_face_create_for_pattern
cairo_ft_font_options_substitute
cairo_ps_surface_dsc_begin_page_setup
cairo_ps_surface_dsc_begin_setup
cairo_ps_surface_dsc_comment
cairo_ps_surface_restrict_to_level
cairo_surface_mark_dirty
cairo_surface_mark_dirty_rectangle
cairo_svg_surface_restrict_to_version

It may be worth having bindings for these, but for now at least it's OK
to just call the Lua-Gnome bindings for them:
gtk.gdk_cairo_region(cr, gtk.new"GdkRegion")
gtk.gdk_cairo_rectangle(cr, event.expose.area)

Interact with bindings for:
FontConfig
FreeType
Pango
Win32 font API

Surface types not supported:
Win32
Quartz
XLib

cairo 1.10 added cairo_device_t, but I don't think how it would make sense to
add bindings for this. E.g. we can't test this since only the gl, xcb and xlib
surfaces uses devices and the test suite can't create such a surface.