python/hetzner: 0.7.5 -> 0.8.0

New features:

 * Support for retrieving reverse PTRs.
 * Support for subnet-ranges.
 * Add logging (aszlig/hetzner#14).

Fixes:

 * Hide internal methods from the public API.
 * Fix Python 3 compatibility.
 * Fix for creating admin accounts with Hetzner's new login site.
 * Fix __repr__/__str__ issue with some exceptions (aszlig/hetzner#23).
 * Fix login for RobotWebInterface

Changes for the hetznerctl utility:

 * show: Show subnets
 * show: Show reverse PTRs
 * New 'rdns' subcommand for getting/setting/removing reverse-PTRs.
 * Use 'argparse' instead of 'optparse'.
 * Add command for managing admin accounts.
 * New '--debug' flag for printing debugging information.

This also fixes NixOS/nixops#778.

Tested building against Python 2.7 and Python 3.6.

Signed-off-by: aszlig <aszlig@nix.build>