color: add support for terminfo-based attributes and color
Using terminfo instead of hard-coding ECMA-48 control sequences provides a
greater assurance that the terminal codes are correct for the current
terminal type; not everything supports the ANSI escape codes.
It also allows us to use a wider range of colors when a terminal emulator
supports it (such as 16- or 256-color xterm), and a few more non-color
attributes, such as the ever-popular blink.