Fix several funky hyperlinks

docs/basics/filesystem.md

@@ -31,7 +31,7 @@ several alternative folders, such as:
  * `modules/civicrm`
 
 Within the `civicrm` folder, there will be a
-[`drupal/`]((https://github.com/civicrm/civicrm-drupal/) or
+[`drupal/`](https://github.com/civicrm/civicrm-drupal/) or
 [`backdrop/`](https://github.com/civicrm/civicrm-backdrop/) subfolder which
 contains the `civicrm.module` along with the role sync modules, blocks, and
 drush and views integration.

docs/basics/skills.md

@@ -72,8 +72,8 @@ accomplishing a particular development goal, certainly vary.
     developers and CiviCRM actually borrows many development practices from
     the project, so learning Drupal is a good place to start if you are unsure.
     -   [Drupal documentation](https://www.drupal.org/docs/)
-    -   [Wordpress documentation]()
-    -   [Joomla documentation]()
+    -   [Wordpress documentation](https://codex.wordpress.org/Main_Page)
+    -   [Joomla documentation](https://docs.joomla.org/)
 -   **SQL / MySQL** - "SQL" is a standardized language used by many different
     kinds of databases to manipulate data in the database. "MySQL" is one kind
     of database which CiviCRM uses to store all its data. The query syntax

docs/extensions/advanced.md

@@ -18,12 +18,10 @@ There are three options to create an ajax or web-service callback:
     your data to *$this-\>ajaxResponse* array and the rest will happen
     automatically. If not, you can directly call
     CRM\_Core\_Page\_AJAX::returnJsonResponse() at the bottom of the run
-    function. See [Ajax Pages and
-    Forms](/confluence/display/CRMDOC/Ajax+Pages+and+Forms)
+    function. See [Ajax Pages and Forms](https://wiki.civicrm.org/confluence/display/CRMDOC/Ajax+Pages+and+Forms)
     documentation.
 -   **Using the API:** Add an API function using `civix`.
-    The API function can be called with the API's [AJAX
-    Interface](http://wiki.civicrm.org/confluence/display/CRMDOC/AJAX+Interface).
+    The API function can be called with the API's [AJAX Interface](http://wiki.civicrm.org/confluence/display/CRMDOC/AJAX+Interface).
     This automatically handles issues like encoding and decoding the
     request/response.
 

docs/extensions/troubleshooting.md

@@ -14,7 +14,7 @@ writers encounter.
 
 ## Extension not doing anything
 
-[]( ###### arguably this list should be removed altogether?? #### )
+<!-- TODO: arguably this list should be removed altogether?? -->
 
 Q: I've created the files and edited them but I don't see the expected
 changes.