feat: add range rule

[Xstoudi]

fix #88

Proposed changes

Add a new rule to check if a number is in a correct range of values.

Types of changes

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• [x] I have read the CONTRIBUTING doc
• [x] Lint and unit tests pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added necessary documentation (if appropriate)

Further comments

I'll be happy to PR the website repository to add the feature to this page if it is okay to you as well : https://preview.adonisjs.com/guides/validator/rules

[thetutlage]

Nice. While I review the PR, can you please add this rule to the doc? For this page https://preview.adonisjs.com/guides/validator/rules

[Xstoudi]

Done! adonisjs/adonisjs.com/84

[thetutlage]

Looks dope!