vm.c: fix sparse warnings

This fixes up all of the sparse warnings in interpreter/vm.c

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Put ktap_dir in ktap.h to fix up sparse warning.

Also make a symbol static in interpreter/transport.c to quiet sparse
some more.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
add doc/TODO.txt

This todo list will record current planed todo item which
waiting to implement in next step.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>