esp32: implement audio sink interface

esp32: add ENABLE_ATT_DELAYED_RESPONSE

added yxml to esp32, max32630-fthr, and stm32-f4discovery-cc256x

pbap_client: add support for md5 authentication challenge

Replaced HCI_PACKET_BUFFER_SIZE with HCI_INCOMING_PACKET_BUFFER_SIZE and HCI_OUTGOING_PACKET_BUFFER_SIZE

esp32: support audio playback via btstack_audio_esp32.c

esp32: enable SCO over HCI

esp32: setup system-wide TLV implementation

esp32: enable le data channels, disable packet logger

esp32: enable le data channels, disable packet logger

esp32: update sdkconfig and use esp_bt.h instead of bt.h

esp32: add HAVE_FREERTOS_TASK_NOTIFICATIONS to fix compile

esp32: fix build of non-btstack examples when added as component to esp-idf. Fixes #85

esp32: support power down and power up. updated sdkconfig

esp32: clone BTstack into esp-idf/components to allow out-of-tree app builds

esp32: prepare example template

esp32: directly call esp_vhci_host_check_send_available instead of tracking callback

esp32: place HCI from VHCI in ringbuffer to avoid blocking VHCI thread

esp32: extract component/btstack, depend on CONFIG_BLUEDROID_ENABLED=n, update README

esp32: More hacks to get send/receive somewhat working

esp32: Add necessary libs, override gitignore .a rule