[PATCH 8/9 V3] Add documentation for the new DTS language.

[Warner Losh]

> I vote against anything similar to the C preprocessor.

The advantage of the current language that's been floated here is that
its 'execution' elements offer a far more expressive macro generation
capability than the cpp.  cpp doesn't have for loops.  There's no way
to convert a number to hex in cpp.  Complicated if statements aren't
possible.  And so on.  m4 allows these things, but imposes
restrictions that make it awkward to use in this context, so it is out
(despite my comments yesterday, and the fact I use it to genreate the
html for my resume).  There's really no other widely available
preprocessor that would be useful here.

Then again, I'm not sure that I completely buy into the mixing data
definitions and execution elements being confusing.  We do that right
now in every C program you write with global variables...  The problem
here is that we're inventing a scripting language to generate data
structures, much like web pages are generated in some scripting
languages by haing the output be html.  There's little confusion
there (and no, I'm not suggesting we use one of them :-).

Warner