Allow underscores in IAM user and group names
This PR solves https://github.com/hashicorp/terraform/issues/9679
My editor also cleaned up a few whitespaces in the docs. If you prefer them removed, please ping me and I update the PR.
@bandesz hi there! Thank you for this.
I wonder if we could also mention in the documentation that the name is actually case-insensitive. It might help some people avoid a possible brown-bag moment.
@kwilczynski sure, I added a second commit and copied the relevant parts from the aws cli documentation.