Add ruby-version and ruby-gemset

Use ruby-1.9.3-p392 and default gemeset for challenges.
Add Gemfile for dependency management

Add rspec to the Gemfile for testing.
Add skeleton for specs

Empty spec file for our Building, Elevator, and Floor models.
Add debugger gem

For debugging configuration and tests.
Add rspec initialiation files and spec_helper

Use spec_helper to require our models.  Since we're outside rails, load
the models in the spec_helper.  Add bundler require statement in
spec_helper.
Add #initialize spec for Building class

Initializing a Building should create a Building with the required
number of Floors and a single Elevator.  Stub out the other models until
we create them.
Add Building definition

Initialize a buidling: create floors and an elevator.  Allow the outside
world to read the number of floors and elevator but not change them.
Add Building#enter spec

When a user calls #enter on a Building object, it should return the
first floor.  Dry up the spec by moving definitions and stubs outside of
the method blocks and make the first floor into a different double in
order to test the #enter method.
Implement Building#enter

Return the first @floor from the Building.
Add Floor#initialize spec

Floors should know their own number.  The number should be readible
publicly.
Add Floor model

Floors should be initialized with their Floor number.  The number should
be publicly readable.
Floors belong_to a building

A floor needs a pointer to the building it belongs to.  In Rails, this
would be a belong_to relation with a foreign key on the Buildings'
table.
Initialize the Floor with a building.
Add self reference when creating Floors

So floors have a reference to Building.  In Rails, we could normally do
this using the shovel operator.
Add Elevator#initialize spec

Elevator belongs to a Building and has a current Floor.  In
ActiveRecord, these would be belong_to relations.
Initial implementation of Elevator

Change #floor to #current_floor for Elevator interface.
Describe call_elevator spec

The #call_elevator method should ask the building to return an elevator.
Delegate call_elevator to the building

Tell the building that we want the elevator on our floor.
Add Elevator#move spec

Move should make the current_floor into the new floor.
Implement Elevator#move

Move should move the Elevator to a new Floor.