Method to convert line breaks into markup

So `"line 1\r\nline 2\r\nline 3"` is converted to Word-compatible markup. This would be used like:

```
_engine.Process("in.docx", "out.docx", new {
    Address = _engine.ConvertLineBreaks("line 1\r\nline 2\r\nline 3")
});
```

It looks like

```
public string ConvertLineBreaks(string in) { return in.Replace(Environment.NewLine, "</w:t></w:r><w:r><w:br/><w:t>"); }
```

will work.
