Preallocate array of best medoids.

Makes a 2x difference!
DOCUMENT ALL THE FUNCTIONS
Schwartzian Transform
Cache denominators in initialization step.

This took 500-object datasets back into the realms of possibility.
Type declarations
Speed up various summations in the init step.
Test k is within range (1,n).

Also specify the exception thrown if k is out of this range;
@test_throws without an exception type is now deprecated.