move config.API to API package

[dustinxie]

Description of the code refactor

Why is this needed

• [] better/less memory usage
• [] reduce running time
• [] clean (easy-to-understand) data structure or algorithm
• [] remove dead code
• [x] better code design or structure (like reduce complexity)
• [x] reduce/decouple dependencies between code modules
• [] increase test coverage
• [x] better code readability