Add further warnings on missing spaces in comments

[melloc]

The spaced-comment rule doesn't warn by default when there isn't a space before */. ESLint 3.x introduced an option, "balanced", which enables warning when it's missing. When we move to a newer ESLint version, we'll want to update the configuration to look like:

module.exports = {
    "rules": {
        ...
        "spaced-comment": [
            "error",
            "always",
            {  
                "block": { "balanced": true }
            }
        ],
        ...
    }
};

Additionally, spaced-comment doesn't warn on lines in multiline comments that are missing a * or a space after a *. For example:

/*
foo
 */

/*
 *foo
 */

There is work being done on a multiline-comment-style option upstream to improve this.

[melloc]

In #4, I updated the config to check both ends of block comments. Using multiline-comment-style will require some further investigation, since it forces multiline comments to be starred blocks, instead of just checking that starred blocks are formatted correctly.