Lock mime-types to ~> 1.25 on Ruby 1.8
Use memoizable
Oh, the things I do for Ruby 1.8 compatibility...

So, it turns out that in Ruby 1.8, methods defined with define_method
return an arity of -1 unless you explicitly state that no arguments are
passed. This breaks memoization, which currently only works on
zero-arity methods.
Update ERD