feat(parser): Add new syntaxic sugar and meaningfull error messages, add more... ✨️

Closes #10 🐔️👍️
Approved-by: v-lafeychine <vincent.lafeychine@proton.me>
Approved-by: aalbert <augustin.albert@bleu-azure.fr>
Approved-by: loutr <loutr@crans.org>

🦀️🍰🦀️🍰🦀️🍰

* fix(parser): Fix the semantics of products without parentheses.

* chore(parser): renaming

* chore(parser & proost): renaming

* feat(parser): documentation

* fix(parser): resolve threads

* feat(parser): Add new syntaxic sugar and meaningfull error messages, add more efficient conversion into terms (VecDeque), remove unused struct ClassicTerm, remove useless & outdated test.
feat(kernel): Add new command: DefineCheckType. eg: "def x:P := P"
feat(proost): Process multiples commands in one line

* feat(parser): Add new syntaxic sugar and meaningfull error messages, add more efficient conversion into terms (VecDeque), remove unused struct ClassicTerm, remove useless & outdated test.
feat(kernel): Add new command: DefineCheckType. eg: "def x:P := P"
feat(proost): Process multiples commands in one line