Added example to usage.md

Added example for using a custom query builder method to usage.md.
Fixes multiple updates on multiple flush executions
Merge pull request #534 from dylanschoenmakers/patch-1

Added example to usage.md
Merge pull request #546 from bobvandevijver/master

Fixes multiple updates on multiple flush executions
Fix immediate doc
More classes exposed as parameters.
Merge pull request #555 from RuslanZavacky/master

More classes exposed as parameters in config.xml
Merge pull request #551 from piotrantosik/patch-1

Fix immediate doc
Merge pull request #549 from ahmedmhmd/master

Ensure non-empty properties under fields mappings in case of auto-mapped objects exists along with manual ones