0.5.2: NULL fix

• Fixed error #22 (InvalidBSON) when using NULL values - @thekid

0.5.1: Aggregation fixes for transactions

• Rewrote count() and distinct() to use aggregation pipelines. See
  https://docs.mongodb.com/manual/core/transactions/#count-operation and
  https://docs.mongodb.com/manual/core/transactions/#distinct-operation
  (@thekid)

0.5.0: Aggregation

• Added new methods Collection::distinct() and Collection::count()
  (@thekid)
• Added new method Collection::aggregate() to perform aggregations, see
  https://docs.mongodb.com/manual/reference/command/aggregate/ and
  https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/
  (@thekid)
• Fixed all places where _id was assumed to always hold ObjectIds.
  (@thekid)

0.4.0: Updates

• Merged PR #1: Implement update operation. Currently supports update operator
  expressions, replacement documents and pipelines will be added later.
  (@thekid)
• Changed insert() to generate and return object IDs if not supplied in
  passed documents. Consistent with how most MongoDB drivers handle this, see
  https://docs.mongodb.com/manual/reference/method/db.collection.insert/#id-field
  (@thekid)

0.3.1: Decimal128 fix

• Fixed large decimal128 number parsing from a string - @thekid

0.3.0: Decimal128

• Added Decimal128 support as specified in http://bsonspec.org/spec.html
  (@thekid)

0.2.0: Database and collections listing

• Added Database::collections() method to list collections in a database
  (@thekid)
• Added MongoConnection::databases() method which lists all databases
  (@thekid)
• Added support for regular expression, UUID and timestamp types
  (@thekid)

0.1.0: Hello world

• First public release - (@thekid)