1st draft of complete class-based std.random successor

[Joseph Rushton Wakeling]

Latest patches rename randomSample => sample, again offering a 
documented alias to assist migration.

It would be nice to complete the set and eliminate randomCover, 
but in this case "cover" seems too vague a name to use.  Any 
suggestions for alternatives?  I wasn't able to readily find an 
equivalent in other random number libraries.

"permutation" seems good to me (or "permute"?), but perhaps 
others have suggestions or can point to a typical naming practice 
from other languages?