[Ur] smlnj build, # comments for .ur files

[Adam Chlipala]

Marc Weber wrote:
> These two topic topic patches are useful to me:
> http://mawercer.de/~marc/urweb-mlton-smlnj-shared-main.patch
>    

Thanks for the patches!  Neither one seems consistent to me with my 
vision for how Ur/Web should be set up, so I'll leave them as something 
folks can apply optionally.

> 1)
> This topic branch allows building the urweb compiler using smlnj.
> the smlnj build of urweb is much faster than mlton.
>    

I build and use Ur/Web with SML/NJ all the time, and have since the 
beginning of the project.  You just have to follow the alternate 
instructions from the manual for using the compiler from the REPL, 
rather than a command line.

> 2)
> this patch implements # comments for urweb
>    

I prefer the lexical simplicity of a single variety of comments, and I 
also prefer that newlines have no significance for parsing.