1. change gap btc args to union to decrease the dram occupied by btc args
2. actually use individual args for every action is the best way(decrease the dram occupy), but for writing code easily and the style, use union
3. gatt server/client should do the same work
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
