1. Actually, btc & api are the same module thing. So the type defined in api header file can be included by btc c/h files.
Besides, why btc & api should be separated, because that user may be aware of api and api refer defines/types, rather than other non-refer things.
All defines/types that user won't use should be put in btc directory (and define with prefix "btc_"), and which will be used by user should be defined with prefix "esp_" .
2. rename attribute value(all is value, not data)
1. which named uuid is esp_bt_uuid_t type
2. which named id is xxx_id_t type, such as service_id_t char_id_t, include inst & uuid
3. share include directory
