Add ayu color theme (with light, dark and mirage variants)
Theme converted from: https://github.com/dempfi/ayu
In the JSON file I added the key _information_for_contributors that works as a comment with relevant information, such as the link to the original repository of the ayu theme, the date of the last update and the license.
Ayu Light:
Ayu Dark:
Ayu Mirage:
