doc: Add missing documentation

[zekth]

Added links to module documentation.
Added fs documentation.

Mention to @axetroy , could you provide an explanation for the options of writeJson module options please?

[axetroy]

@zekth
The options is same with JSON.stringify(value[, replacer[, space]])

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Parameters

/**
      * Converts a JavaScript value to a JavaScript Object Notation (JSON) string.
      * @param value A JavaScript value, usually an object or array, to be converted.
      * @param replacer A function that transforms the results.
      * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
      */
    stringify(value: any, replacer?: (this: any, key: string, value: any) => any, space?: string | number): string;
    /**
      * Converts a JavaScript value to a JavaScript Object Notation (JSON) string.
      * @param value A JavaScript value, usually an object or array, to be converted.
      * @param replacer An array of strings and numbers that acts as a approved list for selecting the object properties that will be stringified.
      * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
      */
    stringify(value: any, replacer?: (number | string)[] | null, space?: string | number): string;

[ry]

LGTM - thanks

I plan on doing some automated documentation at some point, but for the time being this is helpful.

[zekth]

LGTM - thanks

I plan on doing some automated documentation at some point, but for the time being this is helpful.

Once denoland/deno#2089 will land i have a draft for TypeDoc autodocumentation.

[axetroy]

here should be ensureFile