Corrects Competitive Programmer's Handbook and Competitive Programming (#5210)

* #5204 Correct URL, and add direct PDF links to Competitive Programming books.

* Add author to Competitive Programming.

books/free-programming-books.md

@@ -392,8 +392,9 @@
 
 #### Competitive Programming
 
-* [Competitive Programmer's Handbook](https://cses.fi/book.html) - Antti Laaksonen (PDF)
-* [Competitive Programming, 1st Edition](https://cpbook.net/#CP1details) (PDF)
+* [Competitive Programmer's Handbook](https://cses.fi/book/book.pdf) - Antti Laaksonen (PDF)
+* [Competitive Programming, 1st Edition](https://cpbook.net/#CP1details) - Steven Halim [(PDF)](https://www.comp.nus.edu.sg/~stevenha/myteaching/competitive_programming/cp1.pdf)
+* [Competitive Programming, 2nd Edition](https://cpbook.net/#CP2details) - Steven Halim [(PDF)](https://www.comp.nus.edu.sg/~stevenha/myteaching/competitive_programming/cp2.pdf)
 * [Principles of Algorithmic Problem Solving](http://www.csc.kth.se/~jsannemo/slask/main.pdf) - Johan Sannemo (PDF)