Adding timer & alarm for PCF8563 with examples

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Adding timer and alarm for the PCF8563 with examples.

Known limitations:
As the PCF8563 alarm function only uses minute, hour, day and weekday fealds, there are two functions to enable the alarm:

• A DateTime object based function with boolean flags that enable the fealds that should match.
• An explicit one where the alarm can be set by pasing the parameters directly, any value that is out of range will be disabled.