Log Message:
Update to 1.8.0:

Overview of changes from pycairo 1.6.4 to pycairo 1.8.0
=======================================================
General Changes:
    Pycairo 1.8.0 requires cairo 1.8.0 (or later).
    Add documentation (available separately)

Bug Fixes:
    18101: Add support for threading
    18947: cairo.SurfacePattern should INCREF the used surface

New Methods:
    ScaledFont.get_scale_matrix
    Surface.mark_dirty_rectangle
    Surface.set_fallback_resolution

New Constants:
    cairo.EXTEND_PAD
    cairo.HAS_IMAGE_SURFACE
    cairo.HAS_USER_FONT

API Changes:
    Surface.mark_dirty: no longer accepts keyword arguments with default
    values.
    PycairoPattern_FromPattern (C API): has a new 'base' argument - to fix
    #18947.

Other Changes:
    Allow unknown cairo Pattern/Surface types to use the pycairo base
    Pattern/Surface type.