Fixes broken code highlighting in documentation
[FLINK-1327] [core] Fix wrapping of MemorySegments in ByteBuffers
deprecated current aggregation code
Test cases and API for new aggregations
ungrouped aggregations
grouped aggregations
missing license headers
moved AggregationUdf into correct package
name the aggregation operator in the DAG
additional tests for aggregation
CountAggregationFunction does not need an input type
documentation updates
fixed test case
fixed CI build
renamed old aggregation convenience functions
alternative aggregation API
removed author comments
implemented aggregation as Map -> Reduce -> Map
removed aggregation API based on GroupReduce
documentation and test updates