src/oping.c: Improved the help output.
src/oping.c: Improved the help output.

A short description has been added for each option. Also, print the program
version and author.

octo/liboping,iseki-masaya/liboping,barak/liboping,octo/liboping,octo/liboping,iseki-masaya/liboping,iseki-masaya/liboping,octo/liboping,barak/liboping,barak/liboping,iseki-masaya/liboping