add inline logging actions

[DenisCarriere]

• add two new logging actions triggered on:
  • owner balances changes (generate, destroy, transfer, unbind, bind)
  • stat changes (generate & destroy)

// @logging
void logbalances(const name owner, const int64_t drops, const int64_t ram_bytes);

// @logging
void logstat(const int64_t drops, const int64_t ram_bytes);