Expand functions available in xmlio.py

[gnott]

I am putting together some decision letter JATS generation logic (in the https://github.com/elifesciences/decision-letter-parser repo). I remember some logic in one of the other libraries that generates XML, and I tracked it down to the https://github.com/elifesciences/elife-crossref-xml-generation/blob/develop/elifecrossref/tags.py module.

There are some functions in here I'd like to reuse in the decision letter parser project.

Tasks are:

• [x] Copy over useful functions from tags.py over to elifetools/xmlio.py
• [x] Also copy over the test cases for these functions
• [x] After merging to elifetools, then the function calls can be replaced in the elife-crossref-xml-generation library to use them, to avoid code duplication

[gnott]

After some experimentation today, so far the only function to be reused is reparsed_tag(), which I will move over.

I think the rest can remain where they are. Some vary because the output for the Crossref deposit project is different than JATS generation, for example Crossref uses <i> tag and JATS uses <italic>.

If there are other functions to move they can be done later.

[gnott]

Crossref library updated in PR https://github.com/elifesciences/elife-crossref-xml-generation/pull/77, this issue can be closed!