- Turns on compression for in-memory cached data by default
 - Changes the default parquet compression format back to gzip (we have seen more OOMs with production workloads due to the way Snappy allocates memory)
 - Ups the batch size to 10,000 rows
 - Increases the broadcast threshold to 10mb.
 - Uses our parquet implementation instead of the hive one by default.
 - Cache parquet metadata by default.

Author: Michael Armbrust <michael@databricks.com>

Closes #3064 from marmbrus/fasterDefaults and squashes the following commits:

97ee9f8 [Michael Armbrust] parquet codec docs
e641694 [Michael Armbrust] Remote also
a12866a [Michael Armbrust] Cache metadata.
2d73acc [Michael Armbrust] Update docs defaults.
d63d2d5 [Michael Armbrust] document parquet option
da373f9 [Michael Armbrust] More aggressive defaults