v1.3.0

Major changes

• Add support for paging. (#92 by @xuanxu)
• Allow searching by last_updated_date. (#93 by @xuanxu)
• Add submitted_at for submission date querying. (#97)
  This also changes last_updated_date from #93 to updated_at, and similarly for the last_updated and date_submitted sort-by criteria.

Minor changes

• Update Arx() to match new Arx.search signature (from #92). (#94)
• Change incorrect lastUpdated sort-by criterion to lastUpdatedDate. (#96)
• Add to_s methods for Arx::Paper, Arx::Author and Arx::Category. (#99)
• Add fix for JSON warning in Ruby >=2.7. (#101)
• Add contributors section to README.md. (#102)