[server] new API for a better formatting doc

headers/header_spec.txt

src/libraries/utils/markdown.ml

src/libraries/utils/markdown.mli

src/plugins/server/Makefile.in

src/plugins/server/data.ml

src/plugins/server/data.mli

src/plugins/server/doc.ml

src/plugins/server/kernel_ast.ml

src/plugins/server/kernel_fc.ml

src/plugins/server/kernel_project.ml

src/plugins/server/request.ml

src/plugins/server/request.mli

src/plugins/server/server_parameters.ml

src/plugins/server/server_parameters.mli

src/plugins/server/syntax.ml

src/plugins/server/syntax.mli