feat: ignore outputs, providers, resources with comments

Prepend any type of resource, including `resource`, `data`, `module`,
`variable`, and `output` with a comment including "terraform-docs-ignore"
to exclude it from the generated output.

Signed-off-by: Khosrow Moossavi <khos2ow@gmail.com>

examples/main.tf

@@ -63,8 +63,20 @@ data "aws_caller_identity" "ident" {
   provider = "aws.ident"
 }
 
+# terraform-docs-ignore
+data "aws_caller_identity" "ignored" {
+  provider = "aws"
+}
+
 resource "null_resource" "foo" {}
 
+# This resource is going to get ignored from generated
+# output by using the following known comment.
+# terraform-docs-ignore
+# And the ignore keyword also doesn't have to be the first,
+# last, or only thing in a leading comment
+resource "null_resource" "ignored" {}
+
 module "bar" {
   source  = "baz"
   version = "4.5.6"
@@ -84,3 +96,9 @@ module "baz" {
 module "foobar" {
   source = "git@github.com:module/path?ref=v7.8.9"
 }
+
+// terraform-docs-ignore
+module "ignored" {
+  source  = "foobaz"
+  version = "7.8.9"
+}

examples/outputs.tf

@@ -17,3 +17,8 @@ output "output-0.12" {
   value       = join(",", var.list-3)
   description = "terraform 0.12 only"
 }
+
+// terraform-docs-ignore
+output "ignored" {
+  value = "ignored"
+}

examples/variables.tf

@@ -14,6 +14,11 @@ variable "bool-1" {
   default = true
 }
 
+# terraform-docs-ignore
+variable "ignored" {
+  default = ""
+}
+
 variable "string-3" {
   default = ""
 }