[patch:lib] Update Arx() to match new Arx.search signature

[eonu]

Checklist

• All old and new tests pass (ran bundle exec rspec spec in the root directory).
• Read the contribution guidelines.
• Updated documentation (if necessary).

Reason (or issue)

#92 forgot to apply the new start and max_results keyword arguments in Arx.search to the Arx() function.

This raises the question as to whether we really need both Arx.search (and its alias Arx.get) and Arx.

Description

Adds the new keyword arguments to the Arx() function.