Re-synchronization
Issue 533. MkRepoCommits.compare() implemented.
Implementation
Merge branch 'master' into #589
Merge branch 'master' of github.com:aistomin/jcabi-github into Issue-553
Merge branch 'master' of https://github.com/jcabi/jcabi-github into 517
#625 first round. added @NotNull almost everywhere
#625 second round. Added @NotNull to more methods
Merge branch 'master' of https://github.com/jcabi/jcabi-github into 517
Issue 517: code review changes
#625 Added rest of @NotNull

Also, put some puzzles and Ignored some tests.
Nullability test still stays ignored due to bugs.
#625 checkstyle fixes
Issue 383: initial commit
issue #466 RtPullComments should be able to create a new pull comment
#268 iterate() method for MkRepoCommits
#268 style fixes
Issue #636 Randomized tag name for creation and patch
#642 reproduced
#642 fixed
Merge branch 'master' into 625