- Allows serde::timestamp to be used for more common types without
   additional modules.
 - Added serde::timestamp::millis for the cases where greater time
   fidelity is needed in a standardised way (javascript natively
   expects timestamps to be in milliseconds)
 - Included tests for the above
 - Deprecated the timestamp::option module as this achieves the same
   effect seamlessly
 - Maybe expanding this concept to other well-known serde types?

 - Replaces intermediate structs
 - Allows for generic serialising/deserialising from a single function
 - Currently implemented for:
    - Timestamp/TimestampMillis
    - T,Option<T>,Vec<T>,[T] (ser only)