Processed spark-defaults.conf in following steps.
:% s/"\([A-Za-z0-9\-]*\)"\s*\([{=].*\)/\1 \2/gc
:% s/=\(.*\)/= \1/gc
Changed following properties.
1) spark.log.confAsInfo -> spark.logConf
2) spark.ui.retained_stages -> spark.ui.retainedStages
Restored old constructor for spark context, which makes it completely optional to pass
config object to start SparkContext.
Optional configuration to return an Option. Documenting and fixed formatting related nits.