Feature new comment api

[xingstarx]

新的评论功能，包括评论列表展示，添加评论，引用评论

[xingstarx]

不要合并，还没完成呢，代码也需要优化的

[coveralls]

Coverage remained the same at 0.0% when pulling d3747f1 on feature-new-comment-api into c08de93 on master.

[coveralls]

Coverage remained the same at 0.0% when pulling b44ccd0 on feature-new-comment-api into c08de93 on master.

[coveralls]

Coverage remained the same at 0.0% when pulling fc65f65 on feature-new-comment-api into c08de93 on master.

[coveralls]

Coverage remained the same at 0.0% when pulling a634235 on feature-new-comment-api into c08de93 on master.

[coveralls]

Coverage remained the same at 0.0% when pulling e3d682f on feature-new-comment-api into c08de93 on master.

[coveralls]

Coverage remained the same at 0.0% when pulling ea8c137 on feature-new-comment-api into c08de93 on master.