Fix #1157 (Model::has() - ErrorException: Array to string conversion)

With ‘BelongsToMany’ relationships calling the function `Jenssegers\Mongodb\Eloquent\Model::has` can throw an ErrorException with ‘Array to string conversion’.

By flattening the collection here we can avoid triggering the exception.

Issue #1131 fix

- fixed possiblilty to specify index names when creating them
- also fixed docstring comments so code completion works
  properly when using IDEs

* fix query builder delete

* tweak a bit

* tweak the test

Since the function has a check for `! $value` and assigns the MongoDB default of ‘_id’ we should be able to omit the property.

* get the Other/Owner Key name based on different version of Illuminate/Database

* get the Other/Owner Key name based on different version of Illuminate/Database (all relations)

* change function name to more readable

* Add test for multiple level nested dot notation

* Fix multiple level attributes using dot notation

* Mantain parent logic on attribute read for non dot keys

Fixes #1077

Relatinoships -> relationships

* Recursive Convert Dates In Where Clause

* Fix StyleCI

See https://github.com/mongodb/mongo-php-library/issues/171

* add sub document aggregation array functionality

example:
    Model::sum('subarray.*.price');

this method is much simpler as to use as complex raw aggregations

for this function a $unwind directive will be pushed in pipeline before $group

* change testSubdocumentArrayAggregate

change test for different scenarios

* rebase to latest master and fix style ci issues