Provide minimum set of compatibility features required to run code in SICP.

This is a sort of "backburner" project---there's not much yet. Whatever you found missing, send PR.

Once we get enough meat, I'll bundle this to the Gauche distribution.

How to use

Clone the repo, or download zip and extract. Then:

$ ./configure
$ make install

Now, in gosh prompt or Gauche script you can use compat.sicp:

gosh> (use compat.sicp)