Improve documentation by making all of the colors used readable,

Improve documentation by making all of the colors used readable,
no matter what the background color is.

Dark blue on a black background is unreadable, as is yellow on a
light background.  This patch turns on the bright attribute for
colors when on a dark background and turns *off* the bright
attribute when the -W command line option is used (indicating a
_light_ background).  This ensures that text is readable in both
cases.

Patch by: tilghman
Review: https://reviewboard.asterisk.org/r/2224
........

Merged revisions 377509 from http://svn.asterisk.org/svn/asterisk/branches/1.8

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@377510 65c4cc65-6c06-0410-ace0-fbb531ad65f3