Type conversions are not applied for Modelish::Base#[]

[maeve]

Given the following modelish object:

class MyModel < Modelish::Base
  property :my_prop, :type => Integer
end

model = MyModel.new(:my_prop => "42")

When you access the property through the auto-generated accessor, it will perform the type conversion, but if you access the property through the square-bracket hash syntax, it returns the raw, unconverted value:

model.my_prop
# => 42
model[:my_prop]
# => "42"

The Modelish::Base#[] method is currently borrowed from hashie. We need to re-implement it to support modelish-specific concepts like property types (this will probably entail refactoring the property type code as well).