Add width utility functions to avoid incorrect usage of bare log2Ceil(). (#819)

* Add width utility functions to avoid incorrect usage of bare log2Ceil().

* Respond to comments:
Remove apply(Data) method.
Change name(s) to signedBitLength, unsignedBitLength.

* Respond to comments - don't be lazy.
Independently calculate the bit length to verify correct operation.

* Respond to comments - return in.bitLength - 0 (not 1) for 0

* Respond to comments - update wdith for signed 0; add explicit tests.

* Add comment expressing zero width wire assumption.