jk format - prettier without any setup

[dlespiau]

It'd be nice to start working towards integrating some common toolchain-things in jk itself. This is taking the nice properties of the go toolchain which integrates linting, formatting, testing, ... and doesn't need the user to do anything.

We could:

• embed prettier in the standard library and call it from a jk format command
• ship a default config file
• Allow overrides if the user wants something different, namely local config files take precedence over the embedded one.
• This should work for both js and ts.

[dlespiau]

prettier offers a compiled standalone.js package (https://prettier.io/docs/en/browser.html):

• It can run without node.js
• It works with es6 modules
• API: https://prettier.io/docs/en/api.html

It should be somewhat straight forward to write jk format command built around this standalone.js.