Merge pull request #50 from luizmineo/master

Add socket error handling
Dev version
- Better error handling when a connection with the database is lost. Thanks to [luizmineo](https://github.com/luizmineo) [PR 50](https://github.com/vadimtsushko/mongo_dart/pull/50).
- `Future(List<String>) listCollections()` helper added to Db
- `Future(List<String>) listDatabases()` helper added to Db
v0.1.40
Bufgixes for issues 51, 48
v0.1.41
Additional checks and descriptive error message against querying closed db
Additional checks and descriptive error message against opening db in opening state, additional tests
Add tailable cursor support
Preliminary support for streaming in Aggregate framerork. Added method `aggregateToStream`
updated for v0.1.44
Skip aggregateToStream test if server older then v2.6
Skip test for aggregateToStream for older servers
Remove solo_ from test
Add sestegra to authors list
Added test for query on DateTime field