Added --nostager option, fixed some bugs

This pull request includes a bug fix for the data:// attack that fixes issues with + and / not being properly URL encoded in base64 strings.
It also includes a bugfix for the "expect://" attack method, as liffy tries to send a payload of "expect://%s:8000/<payloadname>.php", with %s being literally "%s".
Finally, this implements an unstaged version of the expect://, php://input, and data:// attacks, with the --nostager option included to allow legacy staged versions of each attack.