Create `Placement` model.

It records which couple scored which rank for an event. Though it is
fully computable, it is helpful to have the data saved as a model.
Add Couples to Round during feature setup.
Fix specification of `placements` table.
Implement and test single-dance final scoring.
Move "rule_5.feature" to "single.feature"

No sense in making each rule into its own file.
Use gem "byebug" for debugging

That's what you're supposed to use for Ruby 2.0, apparently.
Test single-dance placement for rules 5-8.

There was a bug in which `lowest_sum` was wrapped in an array, even
though it is already an array itself.
Add Documentation using YARD.
Work around step definition bug in `yard_cucumber`

Classes linked with {Class} cause `yard_cucumber` to fail to display the
step definition documentation. Use `Class` instead.
First pass at porting multi-dance scoring.
Create `SubPlacement` model

It stores the placements for `SubEvent` models. The scoring of
single-dance events will need to be changed to create the appropriate
`SubPlacement` models.
Fix typo copied over from website

The World Salsa Federation site I am using as a reference had couple 55
listed twice. Slightly disconcerting that this wasn't caught before...
Begin testing multi-dance scoring
Use Cucumber's `Table#diff!` to simplify steps

It also provides better failure info than a loop of `Array#includes?`
calls.
Order {Sub,}Placement association by rank
Fix rerun cucumber profile.

For some reason, it would not pick up the step definitions unless an
extra `-r features` was added to the arguments.
Install gem 'pry-stack_explorer'
Rename `SubEvent#compute_placements`

To `SubEvent#compute_sub_placements`
Sort placement table by couple number, not rank

Since there cannot be ties in the couple number (unlike with the rank)
this is guaranteed to be consistent.
Auto-increment the `order` of SubEvent factories