delete a duplicated book
add new course
Merge pull request #1102 from N19270/delete-link

delete a duplicated book
Merge pull request #1103 from N19270/add-course

add a new course
Update free-programming-books.md

Handbook of Graph Drawing and Visualization
Merge pull request #1105 from manasij7479/patch-1

Update free-programming-books.md