Merge pull request #78 from jcabi/master

merge to my repo
#751 MkContents.update(): improper usage of JsonPatch.patch()
Merge pull request #79 from jcabi/master

merge to my repo
Merge pull request #80 from jcabi/master

merge to my repo
Merge pull request #81 from lthuangiang/master

Merge pull request #80 from jcabi/master
#684 Added RtContents.iterate() for directory contents
#684 Fixed PMD error
Merge pull request #759 from lthuangiang/751

#759: pull request #751 MkContents.update(): improper usage of JsonPatch.patch()
Merge pull request #763 from carlosmiranda/684

#763: pull request #684 Added RtContents.iterate() for directory contents
#768 explained Maven 3.1+ requirement