Efetch author extraction refactor

• Simple refactor to make Scrutinizer happy and keep the 10 score.

Fetch more info

• Fetch authors' emails from affiliations when possible
• Format affiliations in array
• Have a dedicated Abstract Extrator object in order to have lighter extractors that extend it
• Add source to each resource in order to know where they come from

Refactor and EutilsEsearch

• Refactor to add DocBlocks
• Refactor to fix Scrutinizer bugs
• Added Latest release badge in README
• Added a resource for EutilsEsearch

Affiliations and PubMed website

• Added support for affiliations fetching,
• Added a resource for PubMed website as there seems to be more data on it than on the Id Converter API.

Refactoring

• uses Laravel's array functions

Bug fix

• IdConverter now fetches the right URL

Data Schema Validation

• Added an array validation library called Volan
• Checks all resources to see if they produce valid extracted data
• Updated Extractors for which data extraction was not valid

Bug fix

• Be consistent in the way the journal array key is extracted

Fix bug

Crossref API provides "updates" metadata that have a type. Some unknown types were making the code throw an exception. This has been fixed.

Allow book imports

0.1.2

Apply fixes from StyleCI (#9)