Make whitespace around comment be optional based on commentstring

As mentioned in #33...

Space around comment should be based on commentstring such that with `commentstring=//%s` you get:
```cpp
//var example = "hi";
//var anotherExample = "hello";
```

But with `commentstring=//\ %s` you get
```cpp
// var example = "hi";
// var anotherExample = "hello";
```

Or `commentstring=<!--%s-->` you get
```html
<!--example-->
```

And with `commentstring=<!--\ \ \ %s\ \ \ -->` you get
```html
<!--   example   -->
```