Proposal: strftime-based calendar/datetime formatting

[josevalim]

I have updated the proposal with the developments mentioned in this thread. The custom formatter is gone and now we have a generally more flexible option-based API.

@kip and @Qqwy, can you please review the new sections “Options” and “Calendar extensions”? I would love your thoughts generally but also in particular on this bullet:

@josevalim

• hours_in_am_pm/3 - it will receive the hours, minutes and second and return a tuple with {hours, :am | :pm | :noon | :midnight} where hours is the equivalent hours if the day was divided in two, at midnight and noon. Note :midnight and :noon must be returned for disambiguation in different locales

Thanks!