raspberrypi-ua-netinst v2.0.0 RC2

RC2 notice:

• This version should work without any limitations!
  Report results in #88.

Thanks for all your support and feedback!

Known bugs:

• root_ssh_pwlogin configuration variable not working in stretch

Changelog:

• support for Debian 9 (stretch)
• support boot or/and install from USB mass storage
• added or changed configuration variables
  • release is set to "stretch" by default
  • disable IPv6

Bugfixes:

• visual LED notification on Raspberry Pi Zero (W)
• fix log output chopping
• leave screen always on during installation