Added the gifify function.

This allows to convert a .mov file into an animated GIF file. Based on
these resources:
* https://gist.github.com/SlexAxton/4989674
* https://gist.github.com/paulirish/b6cf161009af0708315c

plugins/available/gif.plugin.bash

@@ -0,0 +1,34 @@
+cite about-plugin
+about-plugin 'gif helper functions'
+
+# From https://gist.github.com/SlexAxton/4989674#comment-1199058
+# Requirements (Mac OS X using Homebrew): brew install ffmpeg gifsicle imagemagick
+function gifify {
+  about 'Converts a .mov file into an into an animated GIF.'
+  group 'gif'
+  param '1: MOV file name'
+  param '2: max width in pixels (optional)'
+  example '$ gifify foo.mov'
+  example '$ gifify foo.mov 600'
+
+  if [ -z "$1" ]; then
+    echo "$(tput setaf 1)No input file given. Example: gifify example.mov [max width (pixels)]$(tput sgr 0)"
+    return 1
+  fi
+
+  output_file="${1%.*}.gif"
+
+  echo "$(tput setaf 2)Creating $output_file...$(tput sgr 0)"
+
+  if [ ! -z "$2" ]; then
+    maxsize="-vf scale=$2:-1"
+  else
+    maxsize=""
+  fi
+
+  ffmpeg -loglevel panic -i $1 $maxsize -r 10 -vcodec png gifify-tmp-%05d.png
+  convert +dither -layers Optimize gifify-tmp-*.png GIF:- | gifsicle --no-warnings --colors 256 --delay=10 --loop --optimize=3 --multifile - > $output_file
+  rm gifify-tmp-*.png
+
+  echo "$(tput setaf 2)Done.$(tput sgr 0)"
+}