Added support quick-jumping to web-based documentation

[obicons]

When working on Terraform, I commonly need to jump to documentation. I find myself jumping back and forth between Terraform's documentation and Emacs frequently.

This code adds support for hitting "M-." while the point is positioned at a resource to automatically navigate to Terraform's web-based documentation.

[dod38fr]

For team work in a team where not all people use emacs, it would also be useful to add a comment containing a link to documentation above the resource. I.e. something like:

# https://github.com/cloudposse/terraform-aws-tfstate-backend
module "terraform_state_backend" {
  source = "cloudposse/tfstate-backend/aws"

where the comment was added by terraform-mode.

[dod38fr]

@Fuco1 Thanks a bunch. I'll test this next week :-)