Update free-programming-interactive-tutorials-en.md
alphabetized entries in Chinese pages
Merge pull request #1190 from switchhax/master

Add "4Clojure.com" to the tutorial section
Merge pull request #1193 from sunxb10/master

Alphabetized entries in Chinese pages
Add "CS For All"
Merge pull request #1196 from thrabchak/master

Add "CS For All"
Created 'problem-sets-en.md' #1191

Mainly its the base we all could (and in my opinion should) build on.
Merge pull request #1197 from switchhax/master

Created 'problem-sets-en.md'    for reference: #1191
Added 3 new srcs for problems etc
Added links to another problem sets
Merge pull request #1198 from grogy/problem-sets

Added links to another problem sets
Merge pull request #1200 from switchhax/master

Added 3 new srcs for problems etc