Rename head to head_, as the overlap with Prelude.head is too annoying

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extra : amend_source : a2962800260b164c86df8fbe9adafae61e97dd80
Add partText and partString
Get rid of the Param type alias
Add the FormParam type and FormValue class
Add an example program that uploads a file as a paste to lpaste.net
Simplify some upload details
Simplify again
More docs and simplification
Make language and value constructor names uniform
Get rid of the now-unnecessary language name

--HG--
extra : amend_source : 3d49c4b91243c9bff8cefea49e4bb3ab4051282a