task 378:  implement the methods of MkContent: 1) compareTo, 2) json, 3) patch
Signed-off-by: ahmedxx <zertazert@hotmail.fr>
Merge remote-tracking branch 'upstream/master' into puzzle_378

Conflicts:
	src/main/java/com/jcabi/github/mock/MkContent.java
Merge pull request #649 from ahmedxx/puzzle_378

#649: pull request task 378:  implement the methods of MkContent: 1) compareTo, 2) json, 3)...