"Therefore, since brevity is the soul of wit, and tediousness the limbs and outward flourishes, I will be brief..."
Hamlet, Act 2, Scene 2
This oft used phrase and even more oftly used mechanism was, indeed, first coined by Shakespeare and spoken by Lord Polonius.
However, the meaning that William had behind it is someone under debate, though it is almost certainly a commentary based on the fact that, in order to say this line, Lord Polonius gives a long and flagrant introduction to it, thereby proving himself to be neither witty nor brief.
Even though I personally think the phrase rings' true, I am sure it was used, in that context, to show the character of Polonius.. after all, he does snuff it.