* Added codechef's problem set
A vast range of unique problems, some of which are also part of Indian ICPC Preliminary Rounds and Regionals Rounds.
* Added codedrills' comeptitive problem set
Codedrills is the platform responsible for Indian ICPC contests currently (from 2020-present). It has many original & pure algorithmic problems.
* Add GNU Emacs refcard to more/free-programming-cheatsheets.md file under ide/editors category
* Add alphabetical order and PDF indication for the adding emacs refcard
* Added PDF indication
* Add HackThisSite in CTF and corrected address spelling
* Removed slash from the end of the URL
