The htmlentities gem should do the trick:
require 'rubygems'
require 'htmlentities'
coder = HTMLEntities.new
coder.decode('…') # => "…"
coder.decode('…') # => "…"
coder.decode('¢') # => "¢"
coder.decode('¢') # => "¢"
coder.encode("…", :named) # => "…"
coder.encode("…", :decimal) # => "…"