Merge pull request #61 from jcabi/master

merge to my repo
ticket #620 - Contents#remove() very hard to use
Issue #619 - RtReleaseAsset should be able to stream raw content
Issue #617 - RtReleaseAsset should be able to remove files
Merge pull request #632 from carlos-a-crespo/issue-619

#632: pull request Issue #619 - RtReleaseAsset should be able to stream raw content
site fixed
Merge branch 'master' of github.com:jcabi/jcabi-github
Merge pull request #626 from lthuangiang/620

#626: pull request ticket #620 - Contents#remove() very hard to use
Merge pull request #638 from carlos-a-crespo/issue-617

Issue #617 - RtReleaseAsset should be able to remove files
Merge remote-tracking branch 'upstream/master'
#625 merge master into 625
#625 added @NotNull to mock classes
#625 checkstyle fixes