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

courses/free-courses-en.md

@@ -3,6 +3,7 @@
 * [0 - MOOC](#0---mooc)
 * [Algorithms & Data Structures](#algorithms--data-structures)
 * [Android](#android)
+* [APL](#apl)
 * [Artificial Intelligence](#artificial-intelligence)
 * [Assembly](#assembly)
 * [AutoIt](#autoit)
@@ -156,6 +157,14 @@
 * [Programming Mobile Services for Android Handheld Systems: Concurrency](https://www.coursera.org/course/posaconcurrency)
 
 
+### APL
+
+* [APL Course](https://course.dyalog.com) - Dyalog (:construction: *in process*)
+* [APL Cultivation](https://aplwiki.com/wiki/APL_Cultivation) - Adám Brudzewsky
+* [Dyalog APL Tutor](https://tutorial.dyalog.com) - Dyalog
+* [Learn APL with Neural Networks](https://www.youtube.com/playlist?list=PLgTqamKi1MS3p-O0QAgjv5vt4NY5OgpiM) - Rodrigo Girão Serrão 
+
+
 ### Artificial Intelligence
 
 * [AI Courses](https://software.intel.com/content/www/us/en/develop/topics/ai/training/courses.html) - Intel Corporation