some headers cleanup try to not include headers from headers, and remove some redundant include. This helps in modularizing the codebase and also helps during incremental compilations.

remove imsg_borrow_str it's redundant due to ibuf_borrow_str()

send the reply code and meta in a single imsg

inline dispatch_imsg(); start to use some newer imsg api

move includes back to the root directory Splitting stuff into sub-directories was just a big mistake.