Add four new sets of fast quotient and remainder operators

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.