Implementation of temporal type and operators

Type system:

- [ ] Type mapping
- [ ] time
- [ ] date - java.time.Instant
- [ ] time_period - java.time.Instant + java.time.Instant / java.time.Instant + java.time.Period?
- [ ] duration - java.time.Period
- [ ] Serialization/Deserialization examples
- [ ] Timezone gotchas
- [ ] Operators

**Notes:**
The manual points out that the time is the root time, and represents time interval (`start`, `end`). It should support shift, mutation of start / end values, split and so on.

The date is defined as a time with `start = end`.

The time period is a _"non-overlapping time interval"_ with a _"regular duration"_. The regular duration is only relevant for months (varying number of days) and days (timeshifts). It seems the intent is to represent duration in time, such as 2018W1 (first week of 2018) or 2020Q1 (first quarter of 2020).