[racket] reworked html-template

In case anyone is using PLaneT package "neil/html-template"...

I've released a non-backward-compatible version that reworks the 
template language.  The reworking had to be done.  I expect future 
changes to the language to backward-compatible.

http://www.neilvandyke.org/racket-html-template/

BTW, this version also has an internal overhaul to facilitate a 
(not-yet-released) separate package that has some additional 
optimization specific to the Racket Web Server, so I plan to release 
that separate package soon.  You can already use the current version of 
"html-template" with the Racket Web Server, of course, if you give 
"html-template" an output port to write to.

Neil V.