docs(numpydates): add comprehensive docstrings for NumpyDates types

Add module docstring and detailed docs for Unit enum and datetime/
timedelta types (DateTime64, InlineDateTime64, TimeDelta64,
InlineTimeDelta64), including accepted constructor inputs and unit
references. Document supertypes AbstractDateTime64 and
AbstractTimeDelta64. No functional changes.

Author: Christopher Doris

src/NumpyDates/AbstractDateTime64.jl

@@ -1,3 +1,8 @@
+"""
+    abstract type AbstractDateTime64 <: Dates.TimeType
+
+Supertype for [`DateTime64`](@ref) and [`InlineDateTime64`](@ref).
+"""
 abstract type AbstractDateTime64 <: Dates.TimeType end
 
 function Dates.value(d::AbstractDateTime64)

src/NumpyDates/AbstractTimeDelta64.jl

@@ -1,3 +1,8 @@
+"""
+    abstract type AbstractTimeDelta64 <: Dates.Period
+
+Supertype for [`TimeDelta64`](@ref) and [`InlineTimeDelta64`](@ref).
+"""
 abstract type AbstractTimeDelta64 <: Dates.Period end
 
 function Base.isnan(d::AbstractTimeDelta64)

src/NumpyDates/DateTime64.jl

@@ -4,7 +4,14 @@
     DateTime64(value, [unit])
     DateTime64(value, format, [unit])
 
-Construct an `DateTime64` with the given value and unit.
+Construct an `DateTime64` with the given `value` and [`unit`](@ref Unit).
+
+The value can be:
+- An `Integer`, in which case the `unit` is required.
+- A `Dates.Date` or `Dates.DateTime`.
+- `"NaT"` or `"NaN"` to make a not-a-time value.
+- An `AbstractString`, which is parsed the same as `Dates.DateTime`, with an optional
+  `format` string.
 """
 struct DateTime64 <: AbstractDateTime64
     value::Int64

src/NumpyDates/InlineDateTime64.jl

@@ -6,7 +6,14 @@
     InlineDateTime64(value, [unit])
     InlineDateTime64(value, format, [unit])
 
-Construct an `InlineDateTime64` with the given value and unit.
+Construct an `InlineDateTime64` with the given `value` and [`unit`](@ref Unit).
+
+The `value` can be:
+- An `Integer`, in which case the `unit` is required.
+- A `Dates.Date` or `Dates.DateTime`.
+- `"NaT"` or `"NaN"` to make a not-a-time value.
+- An `AbstractString`, which is parsed the same as `Dates.DateTime`, with an optional
+  `format` string.
 """
 struct InlineDateTime64{U} <: AbstractDateTime64
     value::Int64

src/NumpyDates/InlineTimeDelta64.jl

@@ -4,7 +4,11 @@
     InlineTimeDelta64{unit}(value)
     InlineTimeDelta64(value, [unit])
 
-Construct an `InlineTimeDelta64` with the given value and unit.
+Construct an `InlineTimeDelta64` with the given `value` and [`unit`](@ref Unit).
+
+The value can be:
+- An `Integer`, in which case the `unit` is required.
+- `"NaT"` or `"NaN"` to make a not-a-time value.
 """
 struct InlineTimeDelta64{U} <: AbstractTimeDelta64
     value::Int64

src/NumpyDates/NumpyDates.jl

@@ -1,3 +1,13 @@
+"""
+    module NumpyDates
+
+Provides datetimes and timedeltas compatible with Numpy.
+
+See: [`DateTime64`](@ref), [`InlineDateTime64`](@ref), [`TimeDelta64`](@ref) and
+[`InlineTimeDelta64`](@ref).
+
+These can generally be converted to/from their respective types in the `Dates` stdlib.
+"""
 module NumpyDates
 
 using Dates: Dates, value

src/NumpyDates/TimeDelta64.jl

@@ -3,7 +3,11 @@
 """
     TimeDelta64(value, [unit])
 
-Construct a `TimeDelta64` with the given value and unit.
+Construct a `TimeDelta64` with the given `value` and [`unit`](@ref Unit).
+
+The value can be:
+- An `Integer`, in which case the `unit` is required.
+- `"NaT"` or `"NaN"` to make a not-a-time value.
 """
 struct TimeDelta64 <: AbstractTimeDelta64
     value::Int64

src/NumpyDates/Unit.jl

@@ -1,3 +1,16 @@
+"""
+    @enum Unit
+
+The possible time units for datetimes and timedeltas in this module.
+
+Values are: `YEARS`, `MONTHS`, `WEEKS`, `DAYS`, `HOURS`, `MINUTES`, `SECONDS`,
+`MILLISECONDS`, `MICROSECONDS`, `NANOSECONDS`, `PICOSECONDS`, `FEMTOSECONDS`,
+`ATTOSECONDS`.
+
+For compatibility with numpy, the types in this module also accept scaled units as a
+`Tuple{Unit,Int}`. For example `(MINUTES, 15)` for units of 15 minutes. This feature is
+rarely used.
+"""
 @enum Unit::Cint begin
     YEARS = 0
     MONTHS = 1