Support namespaces

[dmytro-savochkin]

Closes feature request #17.

Now if Temping detects you wanted to create a namespace for your model it will create it if it doesn't exist yet or use the existing one. During .teardown it will undefine all the modules from the namespace previously created by itself.

A fresh entry in the Readme:

Temping supports creating models within namespaces.
You can do this either by just including the full namespace in the name:

Temping.create('animal/cat')

Animal::Cat.create # => <Animal::Cat id: 1>
Animal::Cat.table_name # => "cats"
Animal::Cat # => Animal::Cat(id: integer)

Or you can create the module(s) yourself:

module Engineers
  def self.table_name_prefix
    "hard_working_"
  end
end
Temping.create('engineers/developers')

Engineers::Developer.create # => <Engineers::Developer id: 1> 
Engineers::Developer.table_name # => "hard_working_developers"
Engineers::Developer # => Engineers::Developer(id: integer)

Please note that if you create the modules yourself, Temping will NOT attempt
to undefine them when you call Temping.teardown, it will only undefine the modules
created by itself:

module Engineers; end
Temping.create('engineers/developers')
Temping.create('animal/cat')

Temping.teardown

Object.const_defined?(:Engineers) # => true
Object.const_defined?(:Animal) # => false

Deep namespaces are supported as well:

Temping.create('continents/countries/cities/streets/buildings')

# => Continents::Countries::Cities::Streets::Building(id: integer)