* Optimization for expressions that hit a single long column.
There was previously a single-long-input optimization that applied only
to the time column. These have been combined together. Also adds
type-specific value caching to ExprEval, which allowed simplifying
the SingleLongInputCachingExpressionColumnValueSelector code.
* Add more benchmarks.
* Don't use LRU cache for __time.
* Simplify a bit.
* Let the cache grow.
* move parquet-extensions from contrib to core, adds new hadoop parquet parser that does not convert to avro first and supports flattenSpec and int96 columns, add support for flattenSpec for parquet-avro conversion parser, much test with a bunch of files lifted from spark-sql
* fix avro flattener to support nullable primitives for auto discovery and now only supports primitive arrays instead of all arrays
* remove leftover print
* convert micro timestamp to millis
* checkstyle
* add ignore for .parquet and .parq to rat exclude
* fix legit test failure from avro flattern behavior change
* fix rebase
* add exclusions to pom to cut down on redundant jars
* refactor tests, add support for unwrapping lists for parquet-avro, review comments
* more comment
* fix oops
* tweak parquet-avro list handling
* more docs
* fix style
* grr styles
* Prohibit some guava collection APIs and use JDK APIs directly
* reset files that changed by accident
* sort codestyle/druid-forbidden-apis.txt alphabetically
@gianm gauge `emitter/buffers/failed` and `emitter/buffers/totalAllocated` metrics proved to be very inconvenient in practice: they are not additive across a fleet of nodes, are randomly reset when a JVM restarts (that may be completely independent from metrics emitting issues). Regarding [problem identification](https://github.com/apache/incubator-druid/pull/4973#issuecomment-338119125), `emitter/buffers/dropped` serves this well.
Currently in this PR I added `/delta` vs. `/total` metrics, but if there are no objections I would remove `/total` and so align `emitter/buffers/allocated` and `/failed` with `/dropped` and `/events/emitted` which are already delta-only.
David Lim
Gian Merlino
Roman Leventov
Clint Wylie
QiuMM
patelh