Upgraded to rdfjs

[LaurensRietveld]

See #35

What changed:

• Upgraded to N3
• Rdfjs terms instead of strings for query arguments (e.g. the searchTriples function)
• Allow passing a datafactory as argument to fromFile
• Returning rdfjs terms from the functions. Done by looping over the results

What still needs to be done after this PR:

• Update README
• Update type definitions

[RubenVerborgh]

Thanks! Do you happen to have any insights in performance regressions?

[RubenVerborgh]

Implementation looks excellent.

[RubenVerborgh]

Pinging @mielvds and @rubensworks for a review.

Note: is semver major.

[LaurensRietveld]

Didn't do any testing yet (other than the test suite), so can't say much about the performance. Good thing is that the majority of the work in this pr (the test suite) is useful regardless of the solution (c vs js) we end up with.

[rubensworks]

LGTM

[RubenVerborgh]

Thanks a lot @LaurensRietveld. Leaving #45 to do some checks before we release.

[mielvds]

And update the docs...

[RubenVerborgh]

@mielvds Yes, thx: #46