In bignum division, don't compute quotient if not needed, allow overwriting dividend
Improve hashing of bignums
Merge pull request #71 from gambiteer/master

In bignum division, don't compute quotient if not needed, allow overwrit...
Improve exact integer hashing
Improve print_value (used for debugging GC) for symbols
Extend universal backend with keyword objects, continuation objects, string->symbol/keyword, primitive procedure definition