Justification

A common pattern in my codebase is to check for inequalities. But sometimes 13 must be included in the range. The typical solution is to do...

if (is(x).thirteen() && is(x).greater.than.thirteen()) {
  //... something
}

This can be a bit tedious to write and cumbersome for code readability.

Solution

This PR add methods that aggregates the condition into a single convenient function

if (is(x).greater.than.or.equal.thirteen()) {
  //... something
}

The example above allows for a cleaner code, enhancing the readability experience.
This should also benefit other codebases.

Additional Changes

13 new test cases has also been added to ensure that the changes don't break when new functionality is added or existing ones are modified.
I've also noticed that the not operation doesn't have an existing test so I've added one for it for good measure.

is-thirteen$ npm run test

edit: Added sample of tests successfully running