Dropbear 2020.80

[Matt Johnston]

Hi all,

Dropbear 2020.80 is now available to fix a few small issues.

Cheers,
Matt

2020.80 - 26 June 2020

- Don't block authorized_keys logins with no-X11-forwarding or no-agent-forwarding 
  restrictions when X11 or agent forwarding are disabled at compile time.
  This is more of a problem now X11 is disabled by default, reported by Guilhem Moulin

- Reduce binary size by 4kB (x64) when using bundled libtommath

- Define GNU_SOURCE for getrandom() on uclibc, reported by Laurent Bercot and
  Fabrice Fontaine

- Improve checking libtomcrypt version compatibility

- Add some style notes to DEVELOPING.md