Merge pull request #17 from GrandLTU/aggregation-constructors

src/Aggregation/AbstractAggregation.php

src/Aggregation/ChildrenAggregation.php

src/Aggregation/DateRangeAggregation.php

src/Aggregation/ExtendedStatsAggregation.php

src/Aggregation/FilterAggregation.php

src/Aggregation/FiltersAggregation.php

src/Aggregation/GeoBoundsAggregation.php

src/Aggregation/GeoDistanceAggregation.php

src/Aggregation/GeoHashGridAggregation.php

src/Aggregation/HistogramAggregation.php

src/Aggregation/Ipv4RangeAggregation.php

src/Aggregation/MissingAggregation.php

src/Aggregation/NestedAggregation.php

src/Aggregation/PercentileRanksAggregation.php

src/Aggregation/PercentilesAggregation.php

src/Aggregation/RangeAggregation.php

src/Aggregation/ReverseNestedAggregation.php

src/Aggregation/StatsAggregation.php

src/Aggregation/TermsAggregation.php

tests/Aggregation/DateRangeAggregationTest.php