Add support for new time-related display hints

[andresovela]

This PR adds a few time-related display hints:

{:ms}

This prints a timestamp as seconds, considering the input as milliseconds, e.g. a timestamp 1234 prints as 1.234

{:ts}

This prints a timestamp as human-readable time, considering the input is seconds, e.g. a timestamp 123 prints as 00:02:03

{:tms}

This prints a timestamp as human-readable time, considering the input is milliseconds, e.g. a timestamp 123456 prints as 00:02:03.456

{:tus}

This prints a timestamp as human-readable time, considering the input is microseconds, e.g. a timestamp 1234567 prints as 00:00:01.234567

[jonathanpallant]

This looks great - thanks!