Parser implementation & Testing

[xUser5000]

What has been done

• Setup testing environment using Jest.
• Integrate citation-js: I contacted the maintainer of the library on Gitter and he helped me fix the previously mentioned bug. It turns out that WebPack somehow didn't bundle JSON files and this is what caused the problem. I solved the problem by including the .json extension in webpack.config.js. The downside of this workaround is that I will have to update the Webpack config file every time I update the plugin framework. Also, I had to include these lines in packages.json: "browser": {"child_process": false}.
• Added some test cases for the Parser: merely checking for the correctness of some fields and asserting the Parser throws an Error when receiving invalid data.
• Updated README: included a section for screenshots and testing.

[laurent22]

That looks good. Only thing I'm wondering is how complex is the data you will need for the plugin? I guess you'll ignore a good part of what's in the bibtex data - for example you won't display the isbn or issn, etc. In that case, what I'd suggest is create a TypeScript interface that contains the property you'll need, and the parse method would return this structure.

I expect it's quite easy to write this interface, and doing so will have many benefits:

• Type errors are caught during development rather than once the plugin has been released.
• If you use an editor like VSCode you'll get auto-completion, which also makes development easier.

If you need more info about this let me know. You don't need to add the interface in this pull request, it can be in a separate one.