added postgrest-docs-linkcheck; clean up links

* removed outdated links
* updated permanent redirections
* updated postgres docs links to current version
* sort links in ecosystems by repo-name
* change http:// to https://

how-tos/casting-type-to-custom-json.rst

@@ -4,11 +4,11 @@ Casting a type to a custom JSON object
 :author: `steve-chavez <https://github.com/steve-chavez>`_
 
 While using PostgREST you might have noticed that certain PostgreSQL types translate to JSON strings when you would
-have expected a JSON object or array. For example, let's see the case of `range types <https://www.postgresql.org/docs/11/rangetypes.html>`_.
+have expected a JSON object or array. For example, let's see the case of `range types <https://www.postgresql.org/docs/current/rangetypes.html>`_.
 
 .. code-block:: postgres
 
-   -- example taken from https://www.postgresql.org/docs/11/rangetypes.html#RANGETYPES-EXAMPLES
+   -- example taken from https://www.postgresql.org/docs/current/rangetypes.html#RANGETYPES-EXAMPLES
    create table reservations (
      room   int
    , during tsrange

how-tos/providing-images-for-img.rst

@@ -38,7 +38,7 @@ We can retrieve this image in binary format from our PostgREST API by requesting
 Unfortunately, putting the URL into the :code:`src` of an :code:`<img>` tag will not work.
 That's because browsers do not send the required header.
 
-Luckily, we can configure our `Nginx reverse proxy <../admin.html>`_ to fix this problem for us.
+Luckily, we can configure our :ref:`Nginx reverse proxy <admin>` to fix this problem for us.
 We assume that PostgREST is running on port 3000.
 We provide a new location :code:`/files/` that redirects requests to our endpoint with the :code:`Accept` header set to :code:`application/octet-stream`.