parsers: add crossref api parser

[vbalbp]

Signed-off-by: Victor Balbuena vbalbp@gmail.com

Description

Related Issue

Motivation and Context

Checklist:

• [ ] I have all the information that I need (if not, move to RFC and look for it).
• [ ] I linked the related issue(s) in the corresponding commit logs.
• [ ] I wrote good commit log messages.
• [ ] My code follows the code style of this project.
• [ ] I've added any new docs if API/utils methods were added.
• [ ] I have updated the existing documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[vbalbp]

The xml has the following additional information compared to json:

        <crm-item name="publisher-name" type="string">Institute of Electrical and Electronics Engineers (IEEE)</crm-item>
        <crm-item name="prefix-name" type="string">Institute of Electrical and Electronics Engineers</crm-item>
        <crm-item name="member-id" type="number">263</crm-item>
        <crm-item name="citation-id" type="number">94433734</crm-item>
        <crm-item name="journal-id" type="number">5435</crm-item>
        <crm-item name="deposit-timestamp" type="number">20180212160014172</crm-item>
        <crm-item name="owner-prefix" type="string">10.1109</crm-item>
        <crm-item name="last-update" type="date">2018-02-12T22:42:58Z</crm-item>
        <crm-item name="created" type="date">2017-11-23T19:07:49Z</crm-item>
        <crm-item name="citedby-count" type="number">1</crm-item>

However, The 'prefix-name', 'member-id' and 'citedby-count' fields are also in the json result.

On the other hand, json has the field "references-count":13, which gives you the number of references in the record, and which is not found in the xml result (You can always count the references, though).

Apart from that, the rest of the fields are just a mapping from one format to the other, and there is no other extra information in any of them. For that reason, I chose to parse elements as a json result instead of xml since it's easier to parse and more similar to our current json format in labs.