v4.1.0

Changes from v4.0.0:

• Add grouped option for table.objects() method to export nested data. (thanks @lsh!)
• Add shuffle option for the sample() verb. All sampled tables are now shuffled by default.
• Add op.parse_json and op.to_json functions for wrangling JSON string data.
• Add op.map_agg and op.entries_agg aggregate functions, similar to the existing op.object_agg.
• Add columns option for table.objects and table.print output.
• Update table.get(column, row) to default to row index 0 if row is unspecified.
• Update aggregate value collector to avoid unnecessary array copies.
• Fix table expression code generation for computed object keys ({['a'+'b']: 'c'}).
• Fix aq.table() bug with Map input.