Lots of work. Tested in Gambit. poly div works. Ex 2.94 done.
Created new file, generic.scm

I had to comb through chapter-2.scm every time I started up gambit-scheme to
load code into the REPL before testing my latest exercises. Since the
data-driven generic procedure system is used in so many sections and it wasn't
all together, I decided to organize it in a separate file. I also have
implementations for `put` and `get` in this file, modified slightly from a
StackOverflow answer that I found.