Version constraints configuration

terraform-docs version constraints is almost identical to the syntax
used by Terraform. A version constraint is a string literal containing
one or more condition, which are separated by commas.

```yaml
version: ">= 0.13.0, < 1.0.0"
```

Each condition consists of an operator and a version number. A version
number is a series of numbers separated by dots (e.g. `0.13.0`). Note
that version number should not have leading `v` in it.

Valid operators are as follow:

- `=` (or no operator): allows for exact version number.
- `!=`: exclude an exact version number.
- `>`, `>=`, `<`, and `<=`: comparisons against a specific version.
- `~>`: only the rightmost version component to increment.

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

go.sum

@@ -104,6 +104,8 @@ github.com/hashicorp/go-sockaddr v1.0.0/go.mod h1:7Xibr9yA9JjQq1JpNB2Vw7kxv8xerX
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+github.com/hashicorp/go-version v1.3.0 h1:McDWVJIU/y+u1BRV06dPaLfLCaT7fUTJLp5r04x7iNw=
+github.com/hashicorp/go-version v1.3.0/go.mod h1:fltr4n8CU8Ke44wwGCBoEymUuxUHl09ZGVZPK5anwXA=
 github.com/hashicorp/go.net v0.0.1/go.mod h1:hjKkEWcCURg++eb33jQU7oqQcI9XDCnUzHA0oac0k90=
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=