This commit introduces 4 new methods for DS3231 devices:
  - DateTime getAlarm1();
  - DateTime getAlarm2();
  - Ds3231Alarm1Mode getAlarm1Mode();
  - Ds3231Alarm2Mode getAlarm2Mode();

The getAlarm methods assume that the alarms are stored
using 24 hour format since this library doesn't support
storing alarms in 12 hour format (DS3231 hardware supports
this).

Updated the DS3231_alarm example to fetch alarm1. Also
improved the formatting of the serial logging.

Handle edge case where the result of calling getAlarm is used to set the alarm
and the mode is set to "Day"

Co-authored-by: Edgar Bonet <edgar-bonet@users.noreply.github.com>