[GRASS5] d.text enhancement

[Hamish]

Moving right along..

I just added some stuff to d.text which hopefully will make it
a bit more useful & standardized.


* added an at= option to place text as a percentage of window
   height/width in the current display frame.

* added support to the color= option for R:G:B triplets

* added a -b flag to allow you to bold text from the command line.


Behaviour is same as before if you don't use the new options.



The common theme here is to be able to resize windows without having to
redo all your text, and have access to whatever colours you want.



enjoy (& let me know if it breaks),

Hamish