Some improvements for the next release

Changed `errorCallback` to `errorHandler` to keep it consistent
Added `.exportData()` method
Added `.importData()` method
Improved `.insert()` method to allow inserting multiple rows
Updated `.remove()` method

Updated `.remove()` to support multiple keys
Import/Export

Improved both `.importData()` and `.exportData()` methods
Changed `.formatResult()` to return the actually data object instead of
`IDBCursor` result
A few improvements
Meta update