Allow additional url parameters

[ewsterrenburg]

Implements #45

• Implemented in Don't see how this can be added to fetchRawStream. This does cover fetchAsk, fetchBindings & fetchTriples, but fetchUpdate is still ignored. Since it wasn't fully clear what the body should be in this case, I decided to leave out fetchUpdate for now.
• Type definitions for URLSearchParams seems less complete and less flexible than https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams describes. I decided to stick with what the type definitions do allow for.
• Please check if the tests make sense like this.

[coveralls]

Pull Request Test Coverage Report for Build 1773198172

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 99.145%

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Totals
Change from base Build 1514978144:	0.07%
Covered Lines:	78
Relevant Lines:	78

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1777425173

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 99.145%

---

Totals
Change from base Build 1514978144:	0.07%
Covered Lines:	78
Relevant Lines:	78

---

💛 - Coveralls

[rubensworks]

Great, thanks! Released as 2.4.0.