fixed typos and cleand up the image tag plugin

plugins/image_tag.rb

@@ -5,7 +5,7 @@
 # Syntax {% image [class name(s)] url [title text] %}
 #
 # Example:
-# {% imaeg left half http://site.com/images/ninja.png Ninja Attack! %}
+# {% ima left half http://site.com/images/ninja.png Ninja Attack! %}
 #
 # Output:
 # <image class='left' src="http://site.com/images/ninja.png" title="Ninja Attack!" alt="Ninja Attack!">
@@ -30,7 +30,7 @@ module Jekyll
     def render(context)
       output = super
       if @img
-        figure =  "<img class='#{@class}' src='#{@img}' alt='#{@title}' title='#{@title}'>"
+        "<img class='#{@class}' src='#{@img}' alt='#{@title}' title='#{@title}'>"
       else
         "Error processing input, expected syntax: {% img [class name(s)] /url/to/image [title text] %}"
       end