Resolve "Add file handling to proost" ✨️

Closes #27, #29 et #36 🐔️👍️
Approved-by: loutr <loutr@crans.org>
Approved-by: aalbert <augustin.albert@bleu-azure.fr>
Approved-by: belazy <aarthuur01@gmail.com>

🦀️🍰🦀️🍰🦀️🍰

* feat(parser): add tests

* Apply 1 suggestion(s) to 1 file(s)

* Apply 1 suggestion(s) to 1 file(s)

* fix(kernel): fix tests

* fix(kernel): fix tests

* clippy

* add tests

* more tests

* feat(proost): tests

* clippy + move tests in kernel

* repl -> evaluator

* ex

* change processor for repl

* add verbose arg

* remove deps

* reference issues

* add issue for search command

* remove commandprocessor trait

* rename repl.rs

* fix error handling when failing to import file

* fix(proost): consider suggestions from review; slight refactor of errors

* chore(parser/commands): better display of the import command

* chore(parser): renaming private functions and correcting some documentation

* feat(proost): add better display for commands and use it instead in the import command display

* fix(proost): adapt proost to new parser behaviour

* fix(parser): make parser produce Builders instead of terms, which prevents evaluating commands too early

* add basic search command

* move pretty printing out of command processor

* functional cyclic dependency test

* better tab

* still buggy, more tests

* better emoji handling

* import file 2/2

* fix tests

* clippy

* import file 1/2: test if files exists

* add convenient command for user

* add import command, not fonctional yet

* clippy

* move command in parser