add multi author support

[noraj]

Is your feature request related to a problem? Please describe.

Can't have multiple author on the same blog.

Describe the solution you'd like

Add multi author support from https://github.com/bob983/hexo-multiauthor

cf. https://github.com/ppoffice/hexo-theme-hueman/wiki/Additional-Features#multi-author and my PR for another theme https://github.com/ppoffice/hexo-theme-hueman/pull/288/files

Describe alternatives you've considered

Custom implem. instead of relying on a plugin.

[ppoffice]

It's out of the scope of this project.