Feature/mongo 2.6.5 dependencies

depsToProjection -> DepsTracker::toProjection
parseDeps -> DepsTracker::toParsedDeps
documentFromJsonWithDeps -> ParsedDeps::extractFields
Will be incorrect if `isNeeded` is falsey -- e.g., `0` or `""` might not do what you want here. See the notes about `.missing()` in `Value`