Change the insert callback to make it more intuitive.

- If the function was called with an array, the callback will have an array (even if the array had one element).
- If it was called with an object, the callback will have an object.
Removed debug code
Merge pull request #116 from kapetan/upstream

Removed debug code
Updated README with lastErrorObject
Merge pull request #117 from kapetan/upstream

Updated README with lastErrorObject
Add missing error handling
lastErrorObject on all the write functions.
Fix the remove callback parameters.
Add the cursor.map function