This new function spawns a program, similarly to awful.spawn, but captures its
output. On each line of output on stdout / stderr, a Lua function is called with
this line. There are different callbacks for stdout and stderr. When both stdout
and stderr are closed, another callback function is called. The intention for
this last callback is "the program is done", because most programs should only
close their output when they exit.
Signed-off-by: Uli Schlachter <psychon@znc.in>
color_strip_alpha was used to insert colors into Pango markup, but it
did not correctly check for valid Pango colors. ensure_pango_color
checks if the color is valid in Pango, and returns a placeholder if it
is not.