core support for status field highlighting (trunk only)

core support for status field highlighting (trunk only)

This provides the core support needed for status field highlighting.
This patch doesn't actually perform status field highlighting for any port,
but provides the core hooks for doing so.

The syntax is:
OPTIONS=hilite_status:{fieldname}/{threshold}/{below}/{above}
where {fieldname} is the name of a status field.
           {threshold} is the value used as the threshold to trigger a display
                             change.  It can also be set to "updown" to trigger
                             a display change whenever it rises or whenever it falls.
                             If you end the threshold value with %, then it signifies
                             that you want to trigger the display change based on the
                             percentage of maximum.
         {below}, {above}
                        are the color or display attribute that you want to use when
                        the field value is underneath the threshold. Supported display
                        fields are:  normal, inverse, bold, black, red, green,
                                         brown, blue, magenta, cyan, gray, orange,
                                         bright-green, yellow, bright-blue, bright-magenta,
                                         bright-cyan, or white.
Valid field names are:
        alignment, armor-class, carrying-capacity,
        charisma, condition, constitution, dexterity,
        dungeon-level, experience-level, experience,
        gold, HD, hitpoints-max, hitpoints, hunger,
        intelligence, power-max, power, score,
        strength, time, title, wisdom

Refer to window.doc for details. Guidebook updates to come later.