Much improved table functions
* Revises properties, definitions in the catalog
* Adds a "table function" abstraction to model such functions
* Specific functions for HTTP, inline, local and S3.
* Extended SQL types in the catalog
* Restructure external table definitions to use table functions
* EXTEND syntax for Druid's extern table function
* Support for array-valued table function parameters
* Support for array-valued SQL query parameters
* Much new documentation
1) Edited the TooManyBuckets error message to mention PARTITIONED BY
instead of segmentGranularity.
2) Added error-code-specific anchors in the docs.
3) Add information to various error codes in the docs about common
causes and solutions.
* Various documentation updates.
1) Split out "data management" from "ingestion". Break it into thematic pages.
2) Move "SQL-based ingestion" into the Ingestion category. Adjust content so
all conceptual content is in concepts.md and all syntax content is in reference.md.
Shorten the known issues page to the most interesting ones.
3) Add SQL-based ingestion to the ingestion method comparison page. Remove the
index task, since index_parallel is just as good when maxNumConcurrentSubTasks: 1.
4) Rename various mentions of "Druid console" to "web console".
5) Add additional information to ingestion/partitioning.md.
6) Remove a mention of Tranquility.
7) Remove a note about upgrading to Druid 0.10.1.
8) Remove no-longer-relevant task types from ingestion/tasks.md.
9) Move ingestion/native-batch-firehose.md to the hidden section. It was previously deprecated.
10) Move ingestion/native-batch-simple-task.md to the hidden section. It is still linked in some
places, but it isn't very useful compared to index_parallel, so it shouldn't take up space
in the sidebar.
11) Make all br tags self-closing.
12) Certain other cosmetic changes.
13) Update to node-sass 7.
* make travis use node12 for docs
Co-authored-by: Vadim Ogievetsky <vadim@ogievetsky.com>