paypro: example - use strict paypro headers.
paypro: fix readme file for better explanation.
paypro: example - add extra arguments for experimentation.
paypro: example - explain extra arguments in readme file.
paypro: example - add --address and --pubkey options. document in readme.
paypro: example - add privkey option. refactor.
paypro: example - remove some comments.
paypro: example - fix request method.
paypro: example - allow user to set options when using example as a module.
Merge pull request #493 from chjj/fix_paypro_example

Fix Payment Protocol Example