lofitime rewrite to use From<T> and Into<T> instead of custom traits

[philiplinden]

• Implements wrapper types for hifitime::Epoch, hifitime::Duration,
  chrono::DateTime<Utc>, and chrono::Duration instead of traits
• Low-friction conversions between hifitime and chrono types using From<T> and Into<T>
• Implementation of common traits like Deref, DerefMut, and Timelike for
  wrapper types
• Simplified SimpleDateLike trait for common date operations. (Honestly this is a crutch to avoid making a full DateLike implementation for the wrapper type.)
• Added a Readme.

Example

Here's an example I'm using to adapt hifitime::Epochs into egui's DatePickerButton, which only works with chrono::NaiveDates.

In this case I don't care about the loss of precision. I want to use the button to select a date and then use this new date as the starting epoch for a precision timer.

1. Wrap the hifitime::Epoch with HifiEpoch to enable simple type conversions to chrono types.
2. Convert the precision epoch to a loose timezone-naive chrono::NaiveDateTime with a simple .into(). This keeps precision up to chrono's limits, which is in the millisecond range. Note that this is no longer inside a wrapper, it's an actual chrono type.
3. Manipulate the struct as a chrono type as if it were chrono all along.
4. Wrap the chrono::DateTime with LofiDateTime to enable simple type conversions back to hifitime types.
5. Use .into() to get the datetime back as a hifitime::Epoch. At this point the epoch only has the precision of chrono but from now on we can use it as a precision epoch with hifitime as if it were an epoch all along.

ui.menu_button("Epoch...", |ui| {
    let hifi_epoch = HifiEpoch(coordinate_time.epoch());
    let chrono_datetime: chrono::NaiveDateTime = hifi_epoch.into(); // convert precision epoch to timezone-aware `chrono::DateTime`
    let mut selected_date = chrono_datetime.date();
    if DatePickerButton::new(&mut selected_date).ui(ui).changed() {
        // Update the Time resource with the selected date
        let new_time = selected_date.and_time(chrono::NaiveTime::from_hms_milli_opt(0, 0, 0, 0).unwrap());
        let new_datetime = new_time.and_utc();
        let lofi_datetime = LofiDateTime(new_datetime);
        coordinate_time.start_epoch = Some(lofi_datetime.into()); // convert new date back to `hifitime::Epoch`
    }
});