Add Support for something different than Strings in Highlighting (FastVectorHighlighter) [LUCENE-6061]

In my application I need Highlighting and I stumbled upon the really neat FastVectorHighlighter. One problem appeared though. It lacks a way to render the Highlights into something different than Strings, so I rearranged some of the code to support that:

https://github.com/Hotware/Lucene-Extension/blob/master/src/main/java/com/github/hotware/lucene/extension/highlight/FVHighlighterUtil.java

Is there a specific reason to only support String[] as a return type? If not, I would be happy to write a new class that supports rendering into a generic Type and rewire that into the existing class (or just do it as an addition and leave the current class be).

---
Migrated from [LUCENE-6061](https://issues.apache.org/jira/browse/LUCENE-6061) by Martin Braun, updated May 09 2016

Start by reading FastVectorHighlighter and the referenced FVHighlighterUtil.java implementation in the external Lucene-Extension project. Compare the existing String[] rendering API with the proposed generic rendering approach, then inspect Lucene's highlighting tests and API conventions; the issue does not identify specific Lucene files or tests, so the completion criteria need clarification.

Written by the indexing model from the issue text.