Add MEDIAN to help.csv and fix building of documentation

Support indexes with nulls last for MEDIAN aggregate

Add MEDIAN aggregate

TestTools should not leave testing thread in interrupted state

Excessive calls to Runtime.getRumtime().gc() cause OOM for no reason

reduces garbage

Use StringUtils.replaceAll() in Function.replace()

Use dateValueFromDate() and nanosFromDate() in parseTimestamp()

Merge code for parsing and formatting timestamp values

Fix 'String index out of range' for numbers with a very little scale in 'to_char'. Issue 115