Loss of precision when initializing Date BSONValue from msSinceEpoch

When using the msSinceEpoch initializer in our BSONValue extension of Date, some precision is lost. This initializer is used by the from method, so we can see the error when retrieving Date s from a document.

e.g.

let d: Document = ["a": Date(timeIntervalSince1970: 0.001)]

expect(d["a"] as? Date).to(equal(Date(timeIntervalSince1970: 0.001)))

Fails with:
expected to equal <1969-12-31 19:00:00.0010>, got <1969-12-31 19:00:00.0000>

There is also a loss of precision in the msSinceEpoch computed property, as it simply truncates as opposed to rounding.