maximumLineLength: Document the required and default values. Fixes #499

Looks like:


### maximumLineLength

Requires all lines to be at most the number of characters specified

Type: `Integer` or `Object`

Values:
 - `Integer`: lines should be at most the number of characters specified
 - `Object`:
    - `value`: (required) lines should be at most the number of characters specified
    - `tabSize`: (default: `0`) considered the tab character as number of specified spaces
    - `allowComments`: (default: `false`) allows comments to break the rule
    - `allowUrlComments`: (default: `false`) allows comments with long urls to break the rule
    - `allowRegex`: (default: `false`) allows regular expression literals to break the rule

JSHint: [`maxlen`](http://jshint.com/docs/options/#maxlen)

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Fixes #499