add color print
switch on color print, user can use set-color-print-on! and
set-color-print-off! to control if printting in color.

It's true on defalt.
make it false by default
make it works like :show-tid, without a globle switch. to turn color print off, user have to untrace a ns and then trace without :with-color flag. This seems not so convenient as a global switch. Which one do you preffer?
Merge pull request #9 from qiuxiafei/master

add color print