Disable link_local_files?

I have a RST file, with bunch of file names, for example:

```
`U1.txt`, `U1rez.txt`
```

These are not real files and I don't want links to these non-existent files. If would be nice if it could be possible to turn this feature off. Or at leas, before linking, restview could check if this file exists or not.

Start by tracing how restview handles the `link_local_files` behavior for reStructuredText links. Check the existing configuration or command-line options and determine whether disabling linking or checking file existence fits the project; done means non-existent names such as `U1.txt` are not linked when the behavior is disabled or the files are absent.

Written by the indexing model from the issue text.