Alternate approach: preserve single spacing and treat img as inline element

This is an alternate approach to the issue identified in https://github.com/einars/js-beautify/pull/403.

It also fixes an issue introduced by https://github.com/einars/js-beautify/pull/403 whereby:
```
<img> <b>content</b>
```
is beautified to be:
```
<img>  <b>content</b>
```

I think it may be more in line with how the rest of the code works.  I leave it up to you to decide which makes more sense.