Implement update operators

[David Lai]

Field Update Operators

• $inc
• $min
• $max
• $mul
• $rename
• $set
• $setOnInsert
• $unset
• $currentDate

Array Update Operators

• $
• $[]
• $[]
• $addToSet
• $pop
• $pull
• $push
• $pullAll

Modifiers

• $each
• $position
• $slice
• $sort

[David Lai]

All implemented, at 0cf44c5