Add support for Algolia search

[TerminalWitchcraft]

Please make sure these boxes are checked before submitting your issue. Thank you!

• I have setuped and configurated the blog according to Hexo official documentation;
• I have read the Theme Wiki carefully and created my own configuration file(_config.yml);
• I have looked up the Issues and found no duplicate issues.

请在发布新Issue之前确保你已经进行了如下工作，谢谢！

• 我已经按照Hexo官方文档中的步骤安装与配置了Hexo；
• 我已经仔细地阅读了主题Wiki并创建了自己的配置文件(_config.yml)；
• 我已经搜索了Issues，并且没有找到类似的问题。

Since there is no free plan available on swiftype, can we expect a replacement for it such as Algolia?

[ppoffice]

Will be available in version 3.0.0.