PR1 review: Add STM32RTC library sources files

[fpistm]

Review of #1

This fix and enhance the preview PR:

• Use scoped enumerations to unified enumerations definitions and hardened the code.
• Init properly members during begin()
• Fix alarm match parameters usage. Before only MATCH_DHHMMSS was partially managed (match only one time not every month). Now all possible Alarm_Match value are handled.
• Remove getHours(void)/getAlarmHours(void) Use same methods with its default parameters value.
  • uint8_t getHours(RTC_AM_PM *period = NULL);
  • uint8_t getAlarmHours(RTC_AM_PM *period = NULL);
• Add private methods to factorize code:
  • syncTime()
  • syncDate()
  • syncAlarmTime()
• Add public methods:
  • end()
  • getPrediv()
  • setPrediv