Add regexp web books for Python, JavaScript, Ruby (#3694)

free-programming-books.md

@@ -745,8 +745,11 @@ Kerridge (PDF) (email address *requested*, not required)
 
 #### Regular Expressions
 
+* [JavaScript RegExp](https://learnbyexample.github.io/learn_js_regexp/) - Sundeep Agarwal
+* [Python re(gex)?](https://learnbyexample.github.io/py_regular_expressions/) - Sundeep Agarwal
 * [Regular Expressions for Regular Folk](https://refrf.shreyasminocha.me) - Shreyas Minocha
 * [RexEgg](http://www.rexegg.com)
+* [Ruby Regexp](https://learnbyexample.github.io/Ruby_Regexp/) - Sundeep Agarwal
 * [The 30 Minute Regex Tutorial](http://www.codeproject.com/Articles/9099/The-Minute-Regex-Tutorial) - Jim Hollenhorst
 * [The Bastards Book of Regular Expressions: Finding Patterns in Everyday Text](https://leanpub.com/bastards-regexes) - Dan Nguyen  *(Leanpub account or valid email requested)*