ipc:sysv:semaphores:semtool

Added semtool program.
ipc:sysv:semaphores:semtool:a summary of APIs

1> ftok()   : generate a unique key
2> semget() : create or access a semphore array set
3> semctl() : manipulate kernel data structure semid_ds fields
4> semop()  : operate the semaphore itself, up/down, lock/unlock