Added cheatsheets for SQL and Python (#4768)

* Added Python Regex Cheatsheet

* Added MySQL cheatsheet

* Added PostgreSQL cheatsheet

* Added SQL heading

* Fixed alphabetical order

* Fixed alphabetial ordering error

free-programming-cheatsheets.md

@@ -10,6 +10,7 @@
 * [Markdown](#markdown)
 * [MongoDB](#mongodb)
 * [Python](#python)
+* [SQL](#sql)
 
 
 ### Clojure
@@ -63,4 +64,11 @@
 ### Python
 
 * [Comprehensive Python Cheatsheet](https://gto76.github.io/python-cheatsheet) - Jure Šorn (HTML)
+* [Python Regex Cheatsheet](https://www.debuggex.com/cheatsheet/regex/python) - Debuggex (HTML)
 * [Python WorldWide Cheatsheet](https://cheatography.com/davechild/cheat-sheets/python/) - Cheatography (Python)
+
+
+### SQL
+
+* [MySQL Cheatsheet](https://s3-us-west-2.amazonaws.com/dbshostedfiles/dbs/sql_cheat_sheet_mysql.pdf) - Database Star (PDF)
+* [PostgreSQL Cheatsheet](https://s3-us-west-2.amazonaws.com/dbshostedfiles/dbs/sql_cheat_sheet_pgsql.pdf) - Database Star (PDF)