v0.4.0

What's Changed

• Make RelatedItem to extend ModsReader by @beatrycze-volk in #18
• Check for values existence in getValues() function by @beatrycze-volk in #19
• Add functions to get first and last element to ModsReader by @beatrycze-volk in #20
• Update README for ver. 0.4.0 by @beatrycze-volk in #21

Full Changelog: v0.3.0...v0.4.0