Add option to set MAX_CONTEXT_URLS in ContextResolver

[mielvds]

Fixes #104

This would allow setting a custom ContextResolver with a different level, for instance 20:

contextresolver = ContextResolver(jsonld._resolved_context_cache, options['documentLoader'], max_context_urls=20)
jsonld.compact(input, context, {"contextResolver": contextresolver})

This is a ok fix, but the contextresolver could use a refactor.

• The cycles parameter in ContextResolver.resolve() is a set(), but can also be an integer.
• It feels like the default contextresolver should be part of the JsonLdProcessor object instead of being created in the method.
• according to the docs, "contextResolver" is "for internal use only", but I'm not sure why that is. @davidlehn @dlongley @BigBlueHat ?

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
lib/pyld
canon.py	218	4	98%	27, 180, 565–566
context_resolver.py	111	11	90%	46–48, 85, 144, 158, 204, 210–212, 236
iri_resolver.py	141	3	98%	307–308, 318
jsonld.py	2444	164	93%	271–275, 356, 393, 398, 408, 425–440, 476–477, 519, 527, 547, 555–556, 664–669, 749–750, 765–766, 826–831, 856–857, 872–873, 883–884, 910, 951, 961, 967–971, 982–983, 1016, 1025, 1032, 1097, 1120, 1142–1144, 1154–1157, 1172, 1195, 1207–1210, 1302, 1314–1317, 1337, 1366, 1399, 1403, 1440, 1483, 1502–1505, 1514, 1563, 1666–1673, 1700–1702, 1728–1731, 1907, 1945, 2353, 2362–2369, 2461, 2488, 2511, 2520, 3096, 3149, 3152, 3215, 3300, 3334, 3342, 3620, 3625, 3627, 3676, 3814–3818, 3884, 3921, 3984, 4219, 4507, 4641, 4675, 4704–4707, 4733–4734, 4917, 4981, 5008, 5082, 5084, 5102, 5200, 5249, 5481, 5483, 5522, 5524, 5533, 5672, 5800, 5887, 6007–6021, 6083, 6085, 6153, 6366, 6372–6376, 6415, 6418, 6508–6509, 6518
lib/pyld/documentloader
aiohttp.py	71	22	69%	29–39, 68, 74, 86, 98–106, 118–121, 138, 153–156
requests.py	49	5	90%	54, 68, 80–88
TOTAL	3222	209	94%

Tests	Skipped	Failures	Errors	Time
1686	50 💤	0 ❌	0 🔥	2m 50s ⏱️