Bumped up document version to 0.5.2 (#310)
Asakusa Gradle Plugin Documents (#301).
0.5.2 Refactoring (#311).
Merge remote-tracking branch 'private/issue/301-doc' into 0.5-develop
Merge remote-tracking branch 'private/issue/310' into 0.5-develop
Merge remote-tracking branch 'private/issue/311' into 0.5-develop