U1db.Document silently ignores key assignment

"document.contents[foo] = bar" has no effect.

This results in needing to write the above code as:
  var temp = document.contents
  temp[foo] = bar
  document.contents = temp

This is annoying and ugly code everytime I want to update a single value.

Proposed solution:
  Allow saving keys directly.

  If for some reason this is absolutely not possible, atleast throw an error or display a warning when an assignment is attempted, as it is clearly not the desired behaviour that the above line of code does absolutely nothing.