BulkSql feature

Added

• Optional options from $config while initializing Driver\Engine. Have more priority, then default options from Driver\Engine
• Array functions in League\Database\Utils namespace, such as:
  ⋅⋅⋅ array_is_assoc
  ⋅⋅⋅ array_depth
  ⋅⋅⋅ array_flatten
  ⋅⋅⋅ array_flatten_assoc
  ⋅⋅⋅is_array_of_type
• BulkSql feature

Read more...

* `BulkInsert`, `BulkReplace` and `BulkDelete` classes 
* `BulkSqlTrait` with `iterateOverItems` method
* `IGeneralSql` and `IBulkSql` interfaces

Fixed

• Methods return types in Utils\Transaction
• League\Database\Utils\Transaction rename method try to attempt

Removed

• hhvm support from travis-ci.yml