Return Pair for Writer's read method

[evilsoft]

A bit more flexible

I really hate the lack of usability with the Writer's read function. I also not like how it removed the Monoid from the log value. This PR now returns a Pair for w.read() with the Monoid wrapped log in the fst and the value in the snd.

With this change we now get the power of a Pair when we are done with the writing. Also it makes more sense as Pair is the canonical Product type.

This is a BREAKING change, will not depreciate, just changing straight away.

[coveralls]

Coverage remained the same at 100.0% when pulling 7651fdb on writer-pair into 0662911 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 6d695e4 on writer-pair into 0662911 on master.

[evilsoft]