JSON:API compliance

[MaSpeng]

While consuming the "ts-json-api" package we discovered a mismatch between the JSON:API specification at the LinkObiect Interface:

json-api/packages/ts-json-api/src/types/shared.ts

Line 13 in 2052dd7

meta: Meta;

The meta key of the LinkObject has to be optional.

Also, we would really appreciate the addition of an interface for the pagination links which is also described in the mentioned specification.

I have already provided a pull request which will address the mentioned topics: #4