add gopter

[fkromer]

Please provide package links to:

• github.com repo: https://github.com/leanovate/gopter
• godoc.org: https://godoc.org/github.com/leanovate/gopter
• goreportcard.com: https://goreportcard.com/report/github.com/leanovate/gopter
• coverage service link (cover.run, gocover, coveralls etc.), example: [![cover.run](https://cover.run/go/github.com/user/repository.svg?style=flat&tag=golang-1.10)](https://cover.run/go?tag=golang-1.10&repo=github.com%2Fuser%2Frepository)

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.

[ceriath]

Please fill in the PR template with all links

[fkromer]

@ceriath

• goreportcardlink

[ceriath]

@fkromer i added the PR template again to the initial PR. Please add all the links

[fkromer]

@ceriath I added the missing links.

[ceriath]

Please fix the issues with
https://goreportcard.com/report/github.com/leanovate/gopter#golint
https://goreportcard.com/report/github.com/leanovate/gopter#ineffassign
https://goreportcard.com/report/github.com/leanovate/gopter#misspell

Besides those minor issues, LGTM

[avelino]

The maintainers will review your PR and notify you and tag it in case any information is still missing. They will wait 30 days for your interaction, after that the PR will be closed.
https://github.com/avelino/awesome-go/blob/master/CONTRIBUTING.md#maintainers