• Add default and options to get_default_database() (#693)
• Bump the version of hacking, setting our flake8 config
• Support read_concern in database.get_collection() (#708)
• Support $toLong operator (#705)
• Fix for {$size: 1} queries on non-existent fields (#711)
• Parse `index` of $arrayElemAt. Fix #607 (#701)
• Implement the $let operator. (#698)
• Implement the $expr operator. (#538)
• Fix some bad indenting
• Fail properly on computing the $size of a missing array. (#697)
• Fix SyntaxWarning about using "is not" with literals
• Add support for mergeObjects operator (#689)
• fix: use group operators in addFields (#690)