JSON support

[tokcum]

Hi,

from the README (apparently, to large extent still just a copy from tree_magic crate), I figure that there is no support for detecting JSON today. However, under TODO, I've found that JSON support might be implemented through additional checkers.

I decided to use tree_magic_mini as it is more up-to-date. So here is my question: do you plan to work on detecting JSON and returning application/json as MIME type? Are you open for other people contributing and what would you expect from the implementation of such a "checker"?

Thanks.