#Fixes #100: Update to schema43

[t-book]

@alycejenni From my tests this PR covers what is needed to update to the last available schema43 (@ datacite api wrapper). In case I forget something I'm happy about your guidance and working on it.

Overview

https://schema.datacite.org/meta/kernel-4.3/

Changes
Addition of optional “affiliationIdentifier”, “affiliationIdentifierScheme”, and “schemeURI” for affiliation
Addition of optional “schemeURI” for funderIdentifier
Addition of “ROR” to allowed values for funderIdentifierType

Since schema43 affilations can look like

<contributor contributorType="Researcher">
      <contributorName>Huber-Bert, Manfred</contributorName>
      <affiliation affiliationIdentifier="https://ror.org/idkfa3" affiliationIdentifierScheme="ROR" schemeURI="https://ror.org">Something</affiliation>
  </contributor>

Instead of the following with scheme42

<affiliation>Something</affiliation>

Hence, my feature request is to upgrade the plugin to use schema43

Possible Solutions
From my tests it works to just bump to schema43 and use it in later code lines as proposed by the PR

ckanext-doi/ckanext/doi/lib/api.py

Line 15 in 59942cf

from datacite import DataCiteMDSClient, schema42

[alycejenni]

Thank you for doing this! Unfortunately there are a few more changes that are needed before we can merge this:

• schema42 is still referenced in test_generate.py, README.md, interfaces.py, and metadata.py
• schemeURI needs to be changed back to schemeUri; ideally we should probably have a test for this but I won't reject a PR without one because we don't currently have one and it's not new functionality
• please make sure you read the contributing guidelines for commits for your new commits

[alycejenni]

@t-book you will probably also want to include the changes from #104, making sure you change rightsURI to rightsUri.