Sort imports!

--HG--
extra : amend_source : b5f755c8838801ea2c22e283f325a881014fdc4c
Ensure that setHeader removes any duplicate/stale headers
Rename and hide some internal modules

--HG--
rename : Network/WReq/Lens/Internal.hs => Network/WReq/Internal/Lens.hs
More consistent import naming
Tiny import tidiness thing
Document the Types module