Add method option for space-before-function-paren

Proposal: Add a new method option for the space-before-function-paren rule to specify whether a method on a class should have a space following it.

Reason: A common coding style for ES2015 is to never add a space after a named function (ie: function name()), but to still always add a space after a class method name, (ie: class A { constructor () {} }). This style is currently not possible to enforce, since methods get lumped in with all named functions.

ESLint Version Tested: 1.10.1

Documentation Example:

/*eslint space-before-function-paren: [2, { "anonymous": "always", "named": "never", "method": "always" }]*/
/*eslint-env es6*/

function foo () {      /*error Unexpected space before function parentheses.*/
    // ...
}

var bar = function() { /*error Missing space before function parentheses.*/
    // ...
};

class Foo {
    constructor() {    /*error Missing space before method parentheses.*/
        // ...
    }
}

var foo = {
    bar () {           /*error Unexpected space before function parentheses.*/
        // ...
    }
};

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[btmills]

@iglvzx you want no-spaced-func (func-call-spacing will replace it in the next minor release)

[iglvzx]

@btmills Thanks!