Proposal: Add option "serializeAlphabetically"

[jhorbulyk]

Currently, by default when serializing an object from json to hjson, the keys of the object are printed out in the order produced by Object.keys() which isn't particularly deterministic. (Or more precisely it is deterministic based on the order in which keys are populated.) However, it is often useful to have hjson keys rendered in a deterministic ordering such as the ordering producted by sort().