Minor improvements

• provide get_connection_status() method
• provide end() method to shut down bluetooth
• add compile time switch for new ESP IDF
• provide set_discoverability() to change BT discovery mode (only for current ESP IDF)
• add additional flag in set_stream_reader to deactivate i2s
• Remove includes of Arduino.h to highlight independence of Arduino API
• New examples with LED and auto shut down on idle
• Clean up compile warnings so that build with warnings ALL will succeed
• Example with set_pin_config
• Correction - Bluetooth devices with address starting 00 did not auto reconnect
• Implement mono downmix thanks to rbuehlma
• Expand to 24 or 32 bits using i2s_config.bits_per_sample thanks to riraosan
• Tracknumber and TrackCount added to Metadata thanks to alexus2033
• Correction which allows restart after calling end() thanks to alexus2033
• Add method to disconnect current connection thanks to ashthespy