Check for titles fully enclosed in an extra `{}`

Authors should enclose in titles only those parts of the title that require special capitalization. For example:

```
title={A Software Package with an {ACRONYM}}
```

Not like

```
title={{A Software Package with an ACRONYM}}
```

A warning for the latter case would be nice, as when authors do it this way it messes up any change in casing made by bibliography packages.