Deprecate --show-all and --hide-all flags

As of `v0.13.0` flags `--show-all` and `--hide-all` are deprecated in
favor of explicit use of `--show` and `--hide`. In other words when
`--show <section>` is used, only `<section>` will be shown. If you want
to show multiple sections and hide the rest you can specify multiple
`--show` flags. The same logic is also applied to `--hide`.

    # show 'inputs' and hide everything else
    $ terraform-docs --show inputs <formatter>

    # show 'inputs' and show 'outputs' and hide everything else
    $ terraform-docs --show inputs --show outputs <formatter>

    # hide 'header' and show everything else
    $ terraform-docs --hide header <formatter>

    # hide 'header' and hide 'providers' and show everything else
    $ terraform-docs --hide header --hide providers <formatter>

Note: Using `--show` or `--hide` CLI flag will completely override the
values from `.terraform-docs.yml`. Example:

    $ cat .terraform-docs.yml
    sections:
      show:
        - inputs
        - outputs

    # example 1: this will only show 'providers'
    $ terraform-docs --show providers .

    # example 2: this will hide 'inputs' and hide 'providers' and show everything else
    $ terraform-docs --hide inputs --hide providers .

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

examples/.terraform-docs.yml

@@ -3,7 +3,6 @@ header-from: doc.txt
 footer-from: footer.md
 
 sections:
-  hide-all: true
   show:
     - header
     - inputs