Add font config properties underline_thickness,
strikeline_position, strikeline_thickness, overline_position,
overline_thickness, and strikeline_position. Overriding the
font specified/calculated values may improve results for some
fonts. Note that strikeline_thickness and overline_thickness
will default to underline_thickness if set.
Withdraw a and link aliases for href. They may serve a
different purpose in the future.