Add four new sets of fast quotient and remainder operators
* libguile/numbers.c (scm_floor_divide, scm_floor_quotient,
scm_floor_remainder, scm_ceiling_divide, scm_ceiling_quotient,
scm_ceiling_remainder, scm_truncate_divide, scm_truncate_quotient,
scm_truncate_remainder, scm_round_divide, scm_round_quotient,
scm_round_remainder): New extensible procedures `floor/',
`floor-quotient', `floor-remainder', `ceiling/', `ceiling-quotient',
`ceiling-remainder', `truncate/', `truncate-quotient',
`truncate-remainder', `round/', `round-quotient', and
`round-remainder'.
* libguile/numbers.h: Add function prototypes.
* test-suite/tests/numbers.test: Add tests.
* doc/ref/api-data.texi (Arithmetic): Add documentation.
* NEWS: Add NEWS entry.