Add support for jsdoc config file path inclusion in task config

[metmajer]

The following patch adds an additional, optional property config to the task config which allows the user to include a JSDoc config file path:

Example:

jsdoc: {
    compile: {
        config: "jsdoc.json",
        src: ["src/**/*.js"],
        dest: "docs/jsdoc"
    }
}

A JSDoc config file can be used to allow markdown in JSDoc tags, see the Use JSDoc: How To Use the Markdown Plugin page for more information.

Sample JSDoc Configuration

The sample is heavily based on jsdoc's conf.json.EXAMPLE and uses the GitHub Flavored Markdown parser plugin.

{
    "tags": {
        "allowUnknownTags": true
    },
    "source": {
        "includePattern": ".+\\.js(doc)?$",
        "excludePattern": "(^|\\/|\\\\)_"
    },
    "plugins": ["plugins/markdown"],
    "markdown": {
        "parser": "gfm"
    },
    "templates": {
        "cleverLinks": false,
        "monospaceLinks": false
    },
    "jsVersion": 180
}