intridea/grape — pull request #550 by dm1try (2014-01-04 23:41:55+00:00)
Title: Add possibility to define reusable params.

Another one concept :)

Examples:
```ruby
helpers do
params :pagination do
optional :page, type: Integer
optional :per_page, type: Integer
end
end

desc "Get collection"
params do
use :pagination
end
```
using module:
```ruby
# shared_params.rb
module SharedParams
extend Grape::ApiHelpers

params :period do
optional :start_date
optional :end_date
end

params :pagination do
optional :page, type: Integer
optional :per_page, type: Integer
end
end
```

```ruby
helpers SharedParams

desc "Get collection"
params do
use :pagination, :period
end
```