Simply service typing: part1
fix
Update service typing: (non_)attached_kind
fix typos in eliom_client wrt service typing
Tests: update wrt service typing
Comment
names are invariant
WIP GADT

wip

Conflicts:
	src/lib/common/eliom_parameter_base.ml
	src/lib/eliom_parameter.server.mli
	src/server/Makefile
Gadt: more covariance