Option to disable inner cache

[srosset81]

I was using a custom document loader which handled cache, because the contexts were frequently updated.

However it took me some time to realize that there was an inner caching mechanism in this library, that bypassed the document loader.

To disable it manually, I did it like this:

this.contextParser = new ContextParser({
      documentLoader: {
        load: async url => {
          const result = await documentLoaderWithCache();
          this.contextParser.documentCache = {};
          return result;
        }
      }
    });

Maybe it would be a good idea to add an option to disable the inner cache ?

Another possibility would be to let the caching mechanism be handled by the document loader (like it is done by the jsonld.js library). But this would be a breaking change...

[rubensworks]

To be honest, I completely forgot that we had this caching mechanism in place...

Delegating the caching to the document loader certainly makes sense, that's probably the cleanest approach going forward.

But in the short-term, an option to always bypass the cache could certainly be added without breaking changes. (happy to accept a PR for this!)