Prerelease 6.0.0-prerelease.0052

ifdef

Tagging version v6.0.0-prerelease.9.10

Merge pull request #2607 from coldays/add_modulo_opeator

Added missing modulo operator to BsonValue

Merge pull request #2572 from JKamsker/bugs/2570-Support-FieldOnly-Va…

…lueTypes

 Add support for ValueTypes that consist only of Fields #2571

Merge pull request #2489 from JKamsker/ReadTransform

Add support for on-the-fly document upgrades

Bump version to 5.0.20

Fix unit tests to 5.0.19

add N limit count

Update appveyor.yml