Add basic i18n support; add customizable social links; using relative path in img() shortcode

[cs-qyzhang]

Issue #2

I forgot to look at zola's doc in detail, the trans() function is good to use. I've refactored the code these days to add i18n support, it is not as simple as I think, currently zola's support to multilanguage isn't well. After some work, it's finally worked! Now in order to visit different language, we can only input URL mannually, we should add an icon in the top to change the language, but I'm not familiar with html/css, so this work will leave to you.:zany_face:

I also added some additional social links, and make it customizable.

In order to be able to specify the image path more conveniently, I added some code to support relative path of image.

You can see the output of this branch in https://jianyue.tech/ and https://jianyue.tech/zh/

Hope you like it!

[justint]

This is an amazing amount of work, thank you for opening this PR!

I'll begin my review and get my feedback to you soon!

[justint]

I've finished my reviews on your changes. Once again thanks for submitting these, this is an awesome collection of updates to Papaya.

Let me know if you're interested and are willing to address the notes yourself, alternatively I'm happy to make the changes myself if you don't feel you have the time.

Once we've finalized the code changes, I would also like to take a pass at some spelling & grammar fixes to the README.

I still need to write out all the content for my own website with Papaya, so I don't think I'll have the time now to add in a language swap icon just yet. I can file a new issue in case someone else would want to take a stab at it first.

[cs-qyzhang]

Thanks for the detailed review! I'm not good at english and a little buzy recently, so it will be glad that you can continue this work.

[justint]

Certainly, thanks again for the great contributions. I've since opened a new issue for the language selector (#6) to leave as an opportunity for others to tackle until if I can find time to do it myself.