TypeScript Connector OBSERVER - v1.0.0-alpha-11

[jgaehring]

As I mentioned in #15 (comment), I decided to split the Observer changes into a separate PR and npm version, since the hotfixes in alpha-10 really need to be released no matter what. The Observer is in good shape, too, but it does introduce minor changes to the API, so it would give us a safe rollback point if push came to shove.

[jgaehring]

Please note that I just force-pushed a change that adds the "git+" to the package.json's repository URL, so that now it is "git+https://github.com/datafoodconsortium/connector-typescript.git". NPM complained that the "git+" prefix was missing when I tried publishing alpha.10 and alpha.11, so I updated it for both releases on the NPM registry. I'll force-push or add another commit to datafoodconsortium/connector-codegen#31 with the updated package.json and package-lock.json as well, so we can be as consistent as possible.

[lecoqlibre]

I found this implementation is a little complicated. I was thinking about something much more simpler like I said in a previous comment.

For me it was just about adding some callback registering methods like registerCallbackForExport and registerCallbackForImport to the Connector class. Store the callbacks in properties like private callbacksForExport: Set<ExportCallback>; and private callbackForExport: Set<ImportCallback>;. Then call the previously registered callbacks in the Connector:export and Connector:import methods.

I think it would be better to trigger the callbacks in the Connector class rather than in the ConnectorImporterJsonldStream/ConnectorExporterJsonldStream as parsers and serializers should just parse and export.

@jgaehring @RaggedStaff