DOC: improve documentation

scenes/dates.py

 # -*- coding: utf-8 -*-
 """
-This module aims to deal with dates
+This module aims to deal with dates.
+
+---
+
+The `datetime.datetime` class is used as internal date type.
+```
+#!python
+dt = datetime.datetime(year=2020, month=12, day=2)
+```
+Is equivalent to:
+```
+dt = str2datetime("02-12-2020")
+dt = str2datetime("2020-12-02")
+dt = str2datetime("02/12/2020")
+```
+
+The `any2datetime` method returns a `datetime.datetime` instance, whatever the input is (`str` or
+`datetime.datetime`).
+```
+dt1 = datetime.datetime(year=2020, month=12, day=2)
+dt2 = str2datetime("02-12-2020")
+dt1_2 = any2datetime(dt1)  # same
+dt2_2 = any2datetime("02-12-2020")  # same
+```
+
+The `get_timestamp` method converts a `datetime.datetime` instance into a number of seconds (int).
+```
+ts = get_timestamp(dt)  # 1606780800.0
+```
 """
 import datetime
 

scenes/spot.py

@@ -185,6 +185,7 @@ class Spot67Imagery(Imagery):
     Spot 6/7 imagery class.
 
     A `Spot67Imagery` instance carries the following `Spot67Source` instances:
+
     - xs: the multispectral channels (Red, Gree, Blue, Near infrared @ 6.0 meters spacing)
     - pan: the panchromatic channel (Visible domain @ 1.5 meters spacing)
     - pxs: the pansharpened channels (Red, Gree, Blue, Near infrared @ 1.5 meters spacing)