Add a sorting on before write example.

Closes #44
Ensure extra field values are correctly casted.

Closes #11.
Fixed array_key_exists() usage in OrderableRows
Merge pull request #50 from silverstripe-iterators/pulls/array_key_exists-sortTable

Fixed array_key_exists() usage in OrderableRows
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Merge pull request #53 from tractorcow/pulls/travis-status

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Update only current record for many_many relations

Fixes #48 but needs more testing. I only checked that it works for one case!
Basic german translation
Merge pull request #55 from derRobert/master

Basic german translation
Merge pull request #54 from jyrkij/fix-48

Update only current record for many_many relations