+ switch for font loading
+ switch for font loading

I assume `Source Code Pro` is for the code highlighting?  So if `highlight:  enable: false` in `_config.yml`, then the unneeded font will not be loaded.  Saves some bandwidth.

If you wish, I can also switch to [jsDelivr CDN](https://github.com/hexojs/hexo-theme-landscape/pull/46) for better performance in China.
howiefh/hexo-theme-landscape-f,sandinmyjoints/hexo-theme-landscape,cgmartin/hexo-theme-bootstrap-blog,howiefh/hexo-theme-landscape-f,1PxUp/Naji,hexojs/hexo-theme-landscape,tommy351/hexo-theme-landscape,takeshik/hexo-theme-landscape,cgmartin/hexo-theme-bootstrap-blog,1PxUp/Naji,sandinmyjoints/hexo-theme-landscape,takeshik/hexo-theme-landscape