Prepare to be able to document our myriad lenses

* Switch cookie lenses to camel case (why oh why do their corresponding
  fields have a different naming convention from every other type?).

* Move the Lens module to Lens.TH, and reinvent Lens as a place of
  re-exportation, where we can attach documentation to each name,
  since haddock cannot help us with this.

--HG--
rename : Network/WReq/Lens.hs => Network/WReq/Lens/TH.hs
extra : amend_source : 2131a52cc88e8cf09ff511d447e6da1f388fd747
More documentation
Replace the deprecated failure package with exceptions
Docs and examples
Clarify relevance of Either
More docs and examples