LastEvaluatedKey implementation

* Improve Query#all to return real all entries
* Improve Query#count to return real count
* Improve Query#each to iterate over batches of entries
* Improve DynamodbAdapter#clear to clear even large tables
Switch Lotus::Utils::Kernel.* to Lotus::Model::Mapping::Coercions.*
Improve benchmark code
Bump version to v0.1.1