Lexer fix

I patched the lexer so it will read characters like #\M-% now (rather
than just #\M- like it would originally).

What's the current plan regarding implementation of numbers?  I figure
small fixed size integers will be packed into the t_scm_word like
other Lisp implementations do, but are you planning on reimplementing
a library like libgmp or just link to it?

Either way, I was thinking about working on adding lexer support for
numbers (unless you think you will be needing it very soon, in which
case I'd recommend you write the core part and leave me some FIXMEs to
work on once it's Good Enough).

-jivera