Reorder and extend glyph attributes

Faint, invisible, struck and fast blink are added as glyph attributes.
Since there's an edit here, let's take the opportunity to reorder them
so that they correspond to the two's power of the corresponding escape
code. (just for neatness, let's hope that property never gets used for
anything.)

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
Render invisible attribute

Implement invisible mode by setting the foreground color to be the same
as the background color. Not rendering anything would also be an
alternative, but this seems less likely to cause surprises in
conjunction with any hacks.

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
Render struck-out attribute

Implement crossed-out text with an XftDrawRect call, similar to how
underline is implemented. The line is drawn at 2/3 of the font ascent,
which seems to work nicely in practice.

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
Making surf compile again with rt.

The clock_gettime patch needs librt to be linked to surf.

Thanks _odie for the hint.
Merge remote-tracking branch 'origin/master'