Moved
- specs/tools/prelude to prelude,
- prelude patches to prelude/patches/
- the "simple" theory to tests/thy_translation/"
- scripts are moved to scripts/

- renamed subtype to subtype_poly
- pi function does not have implicit arguments anymore
- changed a rewrite rule into an axiom
- added wip tuples

- lambdapi.pkg
- no cert_f subfolder everywhere