Add itertoolz.identical to test if sequences are identical element-wise

This problem is actually more tricky--and coming up with a good implementation more challenging--then you might initially expect.  The current implementation was not my first attempt.

Typical application of `identical` is for consistency checks.  Development workflows often have the following progression: (1) make something that works, and (2) make it better.  "Better" can mean more maintainable, more features (that shouldn't change current behavior), different algorithms/techniques/dependencies/etc, or better performance.  Similarly, sometimes data gets ported to a different format (such as a new database), and one often wants to verify the data and processing tools are equivalent to the original.  Unit tests should typically *help* with this, but real data is often messy and has intricacies you may not think to test.  Also, many other developers are paranoid (myself especially), and want to perform consistency checks to verify *exact* behavior in as many (reasonable) ways as possible.