VERSION string between releases is last release suffixed with '+'.
Additionally, use output of git-describe instead of VERSION string, if it is
not empty.

Closes #285.

second while maintaining backward compatibiitiy with integer
arguments.

- Functions warn() and die() replaced by GNU-like error(3) function
- Register cleanup() with atexit(3)
- Functions called by cleanup() are marked with CLEANUP and are not allowed to
  call exit(3)

- New option `-a`: Play animations at startup
- Ctrl-Space toggles animation for all GIF files
- Infinite loop for all animations

- Scale mode is not reset to default value upon image loading anymore
- New default key binding to change mode to scale-down
- Removed scale mode setting from config.h
- Removed -d command line option, as this is now the default at startup

Also removed now obsolete -p command line option; fixes issue #98

Fixes issue #84

- *_SUPPORT enabled in config.h
- XLIBS helper app prints lib flags needed for current settings

- Configurable key and mouse mappings in config.h
- Put event handling code from main.c into events.[ch]