Add ngrams operation

[benjcal]

add N grams operation
https://en.wikipedia.org/wiki/N-gram

this is my first contribution so I'd love any feedback!

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 3 committers have signed the CLA.

✅ benjcal
✅ jg42526
❌ EC2 Default User

---

EC2 Default User seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}