Added support for SPARQL language

[thomasdegroot18]

This is the support for SPARQL based on the W3C SPARQL specifications
https://www.w3.org/TR/sparql11-query/

All of the queries from the specifications are included in the tests and as examples.

[RunDevelopment]

Thank you for this PR @thomasdegroot18!

Before I'll review this, a few minor things:

1. Please move sparql below soy. The list is sorted alphabetically.
2. We use tabs for indentation. This is true for all files: .html, .js, .test.
3. Please remove the g flags from all patterns. Prism will add a g if it has to.
4. Travis failed because you forgot to rebuild Prism. Run npx gulp to rebuild Prism.

I'll properly review your PR soon.

[thomasdegroot18]

Thanks for the quick comments.

I've updated the location, changed everything in tabs now, removed the g flags and reran npx gulp.
Thanks for the update.

[RunDevelopment]

I took another quick look and noticed that you probably used the Turtle language as a base.
Instead of copying the patterns, you can use Prism.languages,extend('turtle', { ... }) to do the copying for you. This will create a (deep) copy of Turtle and allows to change the patterns of your copy. In combination with Prism.languages.insertBefore, you should be able to write your language definition with less redundancy.
Note: You have to require turtle in components.json for this to work.

This is just an idea of mine as someone who has never worked with SPARQL before and hasn't read the spec yet, but:
Couldn't we just do this:

Prism.languages.sparql = Prism.languages.extend('turtle', {
    'keyword' [ /* the 3 new keyword patterns */ ],
    // 'operator': /the pattern/
});

Prism.languages.insertBefore('sparql', 'punctuation', {
    'variable': /[?$]\w+/
});

Turtle and Sparql just look so similar. Please tell me if I got anything wrong. Again, I don't know either language.

Also:

1. We only use single-quoted strings.
2. Please wrap token names in single quotes. This doesn't change anything semantically but it makes the language definitions easier to read in IDEs (different colors). Example:

   'string': {
       pattern: /"(?:[^\\"\r\n\t\b\f])*"|'(?:[^\\'\r\n\t\b\f])*'/,
       greedy: true
   },

3. A lot of the comments are kinda repetitive and describe the behavior Prism more than your patterns, so please remove some.

[thomasdegroot18]

After checking it, the SPARQL spec and the turtle spec are a bit to diverged to extend one onto the other. Due to most of the changes to both of the specs, both are similar but differ quite a lot in the basics.

I've updated the code with the comments about the quotes and the array.

[RunDevelopment]

While it's true that SPARQL and Turtle don't share a lot when it comes to semantics, their syntax is quite similar on purpose:

Most forms of SPARQL query contain a set of triple patterns called a basic graph pattern. Triple patterns are like RDF triples except that each of the subject, predicate and object may be a variable. (source)

Turtle provides levels of compatibility with the N-Triples [N-TRIPLES] format as well as the triple pattern syntax of the SPARQL W3C Recommendation. (source)

Also, extending in Prism doesn't have any strict definitions or restrictions. It's just a way to share common patterns and structures between language definitions. I suggested extending from Turtle because both language definitions seem very similar and because extending generally reduces redundancy across language definitions and the overall bundle size of Prism.

The only differences between Turtle and SPARQL that I see are the actual syntactical differences (new (e.g. variable) and drastically changed (e.g. keyword) patterns) and small differences where you abided to spec more closely than I and the author of #2012 did (e.g. iri) and where you didn't quite adhere to the spec (e.g. string).

I'll make an update to make Turtle adhere to its spec more closely and to fix a few small mistakes I found.

[thomasdegroot18]

Thanks for the update, I will update the code accordingly and update the pull request.

[RunDevelopment]

Looks good! Just a few minor things.

[RunDevelopment]

2 more things and then we can merge this!

[RunDevelopment]

Thank you for contributing!