Feature: i18n of issues

[alessiostalla]

I've added three fields to the Issue class:

• node: to be able to refer to a node and not just a position
• code: a standardized issue code that we can use to categorize issues, as a key for i18n, etc.
• args: an object holding message arguments as strings, to be potentially interpolated in the translated issue message

The "message" field remains with two purposes:

• as a more technical message (e.g. to write to the application log)
• for issues coming from third-party components (e.g. ANTLR), to hold the third-party message

I've also added a test case showing how the feature could be used with a real-world i18n library (i18next).

[alessiostalla]

It's a pain in JS/TS to use a local copy. In theory, in package.json you can put an https:// or file:/ URL instead of the usual version. However, in practice, when I tried it it would randomly use stale versions even if you had changed the source code of the library and rebuilt it. So it's a practice I tend to avoid; maybe today things work better, I don't know.