[Doc-SIG] Substitutions, encoding results

[David Priest]

My substitution file nears completion.  I'll pass it on when I'm done.

So far using substition to insert characters by name more or less works.  
There are a few problems:

1) Some important Unicode characters can not be substituted.  This includes 
several variety of spaces and all the arrow characters.

2) Substitutions can not be against non-white space.  Thus you can not use 
a |sup3| substitution in your text.  You also can not emphasize 
substitutions.

I'll take a look at the code and see if there are obvious solutions to 
these two problems.