Cover all ES Date Formats

[KodrAus]

The date parser needs to provide the current implementation as a default for Format implementations, but also them to override it where the situation is unique, such as with epoch_millis where there's no equivalent chrono format.

• Move parsing onto the Format trait
• Provide a standard implementation
• Overload where necessary
• Ensure the date parser is complete and doesn't produce unexpected results (such as parsing just a . as milliseconds)

[KodrAus]

The Format trait also needs to specify a format method that takes a DateTime and produces a string.

Adding epoch_millis would be a good start since it will probably be the most efficient method to parse.

[KodrAus]

epoch_seconds will be a worthwhile forma tot have too since it'll provide the speed of millis, but without the imprecision at dates before/close to 1970.

[KodrAus]

Other date formats should be fairly easy to add now. Any date mappings that require changing the parse logic, or where there isn't some chrono format that covers it should be opened as separate issues.