extmod/modbluetooth: Make modbluetooth event not a bitfield.

There doesn't appear to be any use for only triggering on specific events,
so it's just easier to number them sequentially.  This makes them smaller
values so they take up only 1 byte in the ringbuf, only 1 byte for the
opcode in the bytecode, and makes room for more events.

Also add a couple of new event types that need to be implemented (to avoid
re-numbering later).

And rename _COMPLETE and _STATUS to _DONE for consistency.

In the future the "trigger" keyword argument can be reinstated by requiring
the user to compute the bitmask, eg:

    ble.irq(handler, 1 << _IRQ_SCAN_RESULT | 1 << _IRQ_SCAN_DONE)

extmod/nimble/modbluetooth_nimble.c

@@ -4,7 +4,7 @@
  * The MIT License (MIT)
  *
  * Copyright (c) 2019 Damien P. George
- * Copyright (c) 2019 Jim Mussared
+ * Copyright (c) 2019-2020 Jim Mussared
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -612,7 +612,7 @@ int mp_bluetooth_gatts_set_buffer(uint16_t value_handle, size_t len, bool append
 
 #if MICROPY_PY_BLUETOOTH_ENABLE_CENTRAL_MODE
 
-STATIC void gattc_on_data_available(uint16_t event, uint16_t conn_handle, uint16_t value_handle, const struct os_mbuf *om) {
+STATIC void gattc_on_data_available(uint8_t event, uint16_t conn_handle, uint16_t value_handle, const struct os_mbuf *om) {
     size_t len = OS_MBUF_PKTLEN(om);
     mp_uint_t atomic_state;
     len = mp_bluetooth_gattc_on_data_available_start(event, conn_handle, value_handle, len, &atomic_state);