def convert(key, block = nil)
      if block.nil? or block.call(key)
        img_tag(key)
      else
        ":#{key}:"
      end
    end
def convert(key, block = nil)
      if block.nil? or block.call(key)
        img_tag(key)
      else
        ":#{key}:"
      end
    end
convert takes in the key to the emoji to be converted and an optional block
 If block is provided, conversion will be done only if this block evaluates to true.