add "easy forth" and "learning apl" (#6197)

* add "easy forth" and "learning apl"

* reorder alphabetically, add authors

books/free-programming-books-langs.md

@@ -270,6 +270,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [A Practical Introduction to APL1 & APL2](http://robertson.uk.net) - Graeme Donald Robertson (PDF)
 * [A Practical Introduction to APL3 & APL4](http://robertson.uk.net) - Graeme Donald Robertson (PDF)
 * [Introduction to College Mathematics with A Programming Language (1978)](http://www.softwarepreservation.org/projects/apl/Books/CollegeMathematicswithAPL) - E. J. LeCuyer (PDF)
+* [Learning APL](https://xpqz.github.io/learnapl/intro.html) - Stefan Kruger (HTML,PDF,IPYNB)
 * [Mastering Dyalog APL](http://www.dyalog.com/mastering-dyalog-apl.htm) (PDF)
 
 
@@ -731,6 +732,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 
 * [A Beginner's Guide to Forth](https://web.archive.org/web/20180919061255/http://galileo.phys.virginia.edu/classes/551.jvn.fall01/primer.htm) - J.V. Noble
 * [And so Forth...](http://ficl.sourceforge.net/pdf/Forth_Primer.pdf) (PDF)
+* [Easy Forth](https://skilldrick.github.io/easyforth/) - Nick Morgan (HTML)
 * [Programming Forth](http://www.mpeforth.com/arena/ProgramForth.pdf) (PDF)
 * [Starting Forth](http://home.iae.nl/users/mhx/sf.html)
 * [Thinking Forth](http://thinking-forth.sourceforge.net)