Update reference documentation. [DATAMONGO-1179]

**[Christoph Strobl](https://jira.spring.io/secure/ViewProfile.jspa?name=cstrobl)** opened **[DATAMONGO-1179](https://jira.spring.io/browse/DATAMONGO-1179?redirect=false)** and commented

Update reference doc for features new in fowler.
Add new-features section to reference doc


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**Referenced from:** pull request https://github.com/spring-projects/spring-data-mongodb/pull/281
