Added the 'solve_frobenius' operator and renamed 'denomination_combinations' to 'count_frobenius'.

Added the 'sequence' and 'tau' operators.

The astronomy operators now don't care which order the arguments are in, except for 'angular_separation', which expects the first two arguments to be astronomical bodies.

The aliquot operators now detect if an amicable number chain has been found and terminate.

Help has been filled in for all constants and most of the units.

Added 'does_list_repeat', 'sequence' and 'tau' operator.

Added the 'esterling' unit.

'hyperop' now has several hard-coded results for trivial cases.

Fixed bugs in 'triplet_prime' and 'horizon_distance'.

And the usual minor bug fixes.