added diagonal dominance functions, update src

[Dakkers]

yep:

• added isRowDD, isColumnDD, isStrictlyRowDD, isStrictlyColumnDD; these functions are useful for numerical stability-related junk.
• wrote appropriate tests
• made matrix.zeros better (realized I originally use Array.push() instead of allocating the right amount of memory using new Array(n)
• updated src/ (the new implementation of the "naive" prime function was not updated in the source)

cc @LarryBattle

[KartikTalwar]

LGTM

[Dakkers]

@LarryBattle :

I've noticed that we're kind of hacky with the square matrix checking. most functions we have don't actually use matrix.isSquare(M) to check if it's a matrix, we just check the first row and hope that the user didn't enter it incorrectly. we should be checking properly. I'll fix this today. a lot of functions also throw the exact same errors, so we could have a private function throw an error if needed.

as for the private method for the for-loops, that's reasonable too. I'll throw that in today as well.

sorry for jumping the gun!

[Dakkers]

there's also a lot of inconsistency with the way errors are thrown. I'll be fixing that too.