Alias #inspect to #to_s

[mcfilib]

[~]
% ruby --version
ruby 2.0.0p195 (2013-05-14 revision 40734) [x86_64-darwin13.0.0]
[~]
% irb
irb(main):001:0> require 'ribimaybe'
=> true
irb(main):002:0> include Ribimaybe::Maybe
=> Object
irb(main):003:0> Maybe(nil)
=> Ribimaybe::Maybe::Nothing
irb(main):004:0> puts Maybe(nil)
Nothing
=> nil
irb(main):005:0>