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)
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