CSHARP-995: Add support for reading the new extended JSON formats added in server 2.6.
CSHARP-995: Adapt to master branch.
added failing maxscan test.
CSHARP-1000: $maxscan should be spelled as $maxScan

SetMaxScan method added $maxscan option instead of $maxScan option which resulted in that option being ignored by mongod.
CSHARP-1001: Fix certain output formats of JsonWriter.
Merge pull request #1 from mongodb/master

do async.