Add new repository: pletter (#2614)

[nealwon]

• Add new repository: pletter

• Add missing period

Please check if what you want to add to awesome-go list meets quality standards before sending pull request. Thanks!

Please provide package links to:

• github.com repo:
• godoc.org:
• goreportcard.com:
• coverage service link (gocover, coveralls etc.)

Very good coverage

Note: that new categories can be added only when there are 3 packages or more.

Make sure that you've checked the boxes below before you submit PR:

• I have added my package in alphabetical order.
• I have an appropriate description with correct grammar.
• I know that this package was not listed before.
• I have added godoc link to the repo and to my pull request.
• I have added coverage service link to the repo and to my pull request.
• I have added goreportcard link to the repo and to my pull request.
• I have read Contribution guidelines, maintainers note and Quality standard.

Thanks for your PR, you're awesome! 👍