Update free-programming-books.md
Merge pull request #1016 from vamseeps/patch-1

The Codingus
Added Explore Flask by Robert Picard
Merge pull request #1017 from yaph/exploreflask

Added Explore Flask by Robert Picard
Add Java(Spring/Spring Boot/Spring Security) Docs.
Merge pull request #1018 from sudoyu/patch-1

Add Java(Spring/Spring Boot/Spring Security) Docs.
Add Machine Learning docs in Japanese.
Merge pull request #1020 from sudoyu/patch-2

Add Machine Learning docs in Japanese.
Update free-courses-en.md

Added Python course by MIT
Update free-courses-en.md

Added Python course from MIT OCW
Merge pull request #1021 from mousebaiker/master

Python course by MIT
Advertise new search engine
Fix typo