Resolve "Pest parser"

Closes #3

Approved-by: belazy <aarthuur01@gmail.com>
Approved-by: aalbert <augustin.albert@bleu-azure.fr>

* fix(parser): Fix minor issues (impl PartialEq for tests)

* feat(parser): Add more inclusive syntax

* feat(parser): Add informative message for free variables

* fix(parser): Fix a conversion bug

* feat(parser,core): Move classic term from core into parser

* feat(parser): Conversion from classic terms to terms

* feat(core): Add conversion from classic term to term

* chore(parser): Rename pest file

* chore(core): Move classic terms in its own file

* feat(parser): Add ClassicTerm with variables for easier user input

* fix(parser): Reorganize lib.rs and parser.rs

* fix(parser): Reorganize lib.rs and parser.rs

* fix(parser): Reorganize lib.rs and parser.rs

* chore(parser): Rename tests files

* chore(parser): Rename tests files

* feat(parser): add parser for terms, commands and files

* feat(parser): add parser for terms, commands and files

* feat(parser): add parser for terms, commands and files

* feat(parser): add parser for terms, commands and files

* feat(parser): add parser for terms, commands and files

* feat(parser): add parser for terms, commands and files

* feat(parser): add parser for terms, commands and files

* chore(core): add license

* chore(parser): remove warnings

* chore(core): format files

* chore(parser): remove warnings

* chore(parser): format code

* fix(core): add lib.rs

* feat(term): Add early Term struct + Display trait

* feat(parser): add parser crate and pest config