Adds a level option to gifsicle

CHANGELOG.markdown

@@ -2,6 +2,7 @@
 
 ## unreleased
 
+* Added options to Gifsicle, specifically --careful (for compatibility) and --optimize for granularity [#51](https://github.com/toy/image_optim/issues/51) [@kaspergrubbe](https://github.com/kaspergrubbe)
 * Speedup specs (~8x) [#60](https://github.com/toy/image_optim/issues/60) [@toy](https://github.com/toy)
 * `script/worker_analysis` to compare worker chains by optimization, time and losslessness [@toy](https://github.com/toy)
 * `Cmd` module to ensure interrupted commands can't go unnoticed [@toy](https://github.com/toy)

README.markdown

@@ -252,6 +252,8 @@ Worker can be disabled by passing `false` instead of options hash.
 
 ### :gifsicle =>
 * `:interlace` — Turn interlacing on *(defaults to `false`)*
+* `:level` — Compression level: `1` - light and fast, `2` - normal, `3` - heavy (slower) *(defaults to `3`)*
+* `:careful` — Avoid bugs with some software *(defaults to `false`)*
 
 ### :jhead =>
 Worker has no options

lib/image_optim/worker/gifsicle.rb

@@ -7,10 +7,20 @@ class Gifsicle < Worker
       INTERLACE_OPTION =
       option(:interlace, false, 'Turn interlacing on'){ |v| !!v }
 
+      LEVEL_OPTION =
+      option(:level, 3, 'Compression level: '\
+          '`1` - light and fast, '\
+          '`2` - normal, '\
+          '`3` - heavy (slower)') do |v|
+        OptionHelpers.limit_with_range(v.to_i, 1..3)
+      end
+
+      CAREFUL_OPTION =
+      option(:careful, false, 'Avoid bugs with some software'){ |v| !!v }
+
       def optimize(src, dst)
         args = %W[
           --output=#{dst}
-          --optimize=3
           --no-comments
           --no-names
           --same-delay
@@ -19,7 +29,10 @@ def optimize(src, dst)
           --
           #{src}
         ]
+
         args.unshift('--interlace') if interlace
+        args.unshift('--careful') if careful
+        args.unshift("--optimize=#{level}") if level
         execute(:gifsicle, *args) && optimized?(src, dst)
       end
     end