Changed the way how (offlineimap) is called. Previously, had to specify "-a <account>" option, which wasn't flexible, especially for hook calls. Also (call-function-maybe) now can accept unlimited number of parameters.
Modified (offlineimap) to, when not given account name, invoke offlineimap in mode to fetch mail from all accounts. Also, implemented (ono-on-stdout); this required adding (system-with-reader) function, that will call user supplied function on every line on stdout.