Add hl.q parameter to HighlightOptions

Add hl.q parameter for HighlightOptions: http://wiki.apache.org/solr/HighlightingParameters#hl.q

Example usage highlighting the word "crime" in all documents after querying by "immigration":

```
si.query("immigration").highlight("text", useFastVectorHighlighter=True, highlightMultiTerm=True).highlight(q="crime").execute().highlighting
```