Added some functionality for using ROPgadget as library

## Features

- Added silent - parameter to the do_XXX functions in the cmd class so that those functions can be called from other scripts while generating no visible output.
- Added gadgets() method to retrieve extracted gadgets.
- Added option to obtain all gadgets(disabling the unique gadget filter).
- Added EOF handler so that the console can be closed using CTRL+D
- Fixed typo
- Gadgets now also stores the bytes disassembled.

## Example:

        # Process file
        scanner = ropgadget.core.Core(ropgadget.args.Args().getArgs([]))
        scanner.do_binary(filename, silent=True)
        scanner.do_depth(str(depth), silent=True)
        scanner.do_all("enable", silent=True)
        scanner.do_load("", silent=True)

        # Get gadgets
        gadgets = scanner.gadgets()
        logger.info("Extracted %d gadgets.", len(gadgets))

        for gadget in gadgets:
            logger.debug("0x%08X: %s bytes: %s", gadget['vaddr'], gadget['gadget'], hex(gadget['bytes']))
            # Do something with it