Converted to big.Rat; except exponents. Squashed:

commit 03faefe15d8a2a327381d26e452772c1156ffcc6
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Tue Feb 19 10:53:03 2013 +1100

    comment out fmt.Prints

commit 80670f82bddfa4d165c88544deccad081434d23b
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Tue Feb 19 10:51:40 2013 +1100

    divide by zero

commit 4e09102f0b9372d944c67df8a170b6d5f4c44b05
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Tue Feb 19 10:48:09 2013 +1100

    less/greater than

commit fb904a56eacce770a950a1f10ca661acbaefe5b0
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Tue Feb 19 10:34:01 2013 +1100

    tests, returns - handle nils correctly

commit bdc380c5d5b9bf95c86ae80a93bcc8d187c9eaba
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Tue Feb 19 00:48:46 2013 +1100

    wip - testing - handle errors

commit 5ac786207a3436142ef5e76044bb11a4c85e5ac0
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Tue Feb 19 00:23:07 2013 +1100

    bigrat, tests started - simple +-*/ working

commit 72e0d9dbd8dcecb03df4294712022904e90de904
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Mon Feb 18 23:52:40 2013 +1100

    evaler refactored to bigrat. Now for tests

commit 874ba9eaaa9651e9535bd12b2830bfdd662c902f
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Mon Feb 18 23:33:27 2013 +1100

    go fmt stack/*

commit 0ef3ecbd725f06fd6a1f601149d4e68785ff0d7c
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Mon Feb 18 23:33:17 2013 +1100

    wip bigrat

commit d83d6915c1294f9449f2faadfb3aaf42d10df42a
Author: Sonia Hamilton <sonia@snowfrog.net>
Date:   Mon Feb 18 23:20:01 2013 +1100

    update readme
update license to bsd-3