Update to current version, support for SSL.

- Fix building with gcc10

- Switch to upstream download url

- Updated to version 0.9.16 which is now part of libvncserver as in
page http://www.karlrunge.com/x11vnc/ there is sentence
x11vnc is a contributed program to the LibVNCServer project at SourceForge.net or
https://github.com/LibVNC/x11vnc
Changes:
* Build fixes.
* Misc. documentation fixes.
* Misc. buffer overflow and memleak fixes.
* Support for OpenSSL 1.1.0.
* Fix for Debian bug #672435.
* Added support for the X Composite Extension. For subwindow/appshare
modes this allows sharing the respective window/app when it
is partially or completely off-screen as XComposite renders
the window contents to an off-screen buffer. Before, updating
of the window contents would stop once it went even partially
off-screen.
* Added XInput 2 multi-pointer support which allows multiple clients
to view and control a single shared screen, all having their
own mouse pointers and keyboard foci. For in-depth info, read
http://edoc.hu-berlin.de/master/beier-christian-2011-07-19/PDF/beier.pdf,
especially section 5.1.

Added some support for running under Wayland via the deskshot utility
found in the misc/ subdirectory.

- miscellaneous new features and changes: