Add APL-related items (#6652)

* Add one APL book

And fix links and notes the some others

* Add APL cheat sheets

* APL courses

* French APL video series

* mark APL Course as in process, add one more course

* mark as in process

* ADSP and Array Cast

* Add APL

* Add APL-related entries

* Add number for sort ordering

* correct number of blank lines between last section and next heading

* Remove trailing slash

* Move book

* Move book and limit URLs to 1 per line

* full URL

* add missing line

* Combine into playlist

* replace multiple links with single link

… which is a redirect to the listing for the latest released version

more/free-programming-playgrounds.md

@@ -1,5 +1,6 @@
 ### Index
 
+* [APL](#apl)
 * [C](#c)
 * [C#](#csharp)
 * [C++](#cpp)
@@ -45,6 +46,14 @@
 * [V](#v)
 
 
+### APL
+
+* [APLgolf](https://razetime.github.io/APLgolf)
+* [ngn/apl](https://abrudz.github.io/ngn-apl)
+* [TryAPL](https://tryapl.org)
+* [TryAPL Mini](https://janiczek.github.io/tryapl-elm)
+
+
 ### <a name="c"></a>C
 
 * [JDoodle - Online C Compiler IDE](https://www.jdoodle.com/c-online-compiler/)