Implement compound-literal value conversion and add tests

[mielvds]

This PR implements support for compound literals in RDF direction (see https://www.w3.org/TR/json-ld-api/#overview-16). It fixes the two related tests in the test-suite:

Parses compound literal with proper option.

• fromRdf#tdi11
• fromRdf#tdi12

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
lib/pyld
canon.py	218	4	98%	27, 180, 565–566
context_resolver.py	103	8	92%	76, 135, 149, 195, 201–203, 227
iri_resolver.py	141	3	98%	307–308, 318
jsonld.py	2491	167	93%	274–278, 361, 398, 403, 413, 430–445, 481–482, 524, 532, 552, 560–561, 669–674, 754–755, 770–771, 831–836, 861–862, 877–878, 888–889, 915, 956, 966, 972–976, 987–988, 1031, 1038, 1103, 1126, 1148–1150, 1160–1163, 1178, 1201, 1213–1216, 1308, 1320–1323, 1343, 1372, 1405, 1409, 1446, 1489, 1508–1511, 1520, 1569, 1672–1679, 1706–1708, 1734–1737, 1913, 1951, 2359, 2368–2375, 2467, 2494, 2517, 2526, 3111, 3147, 3151, 3154, 3208, 3261, 3264, 3327, 3412, 3446, 3454, 3732, 3737, 3739, 3788, 3926–3930, 3996, 4033, 4096, 4331, 4619, 4753, 4787, 4816–4819, 4845–4846, 5029, 5093, 5120, 5194, 5196, 5214, 5312, 5361, 5593, 5595, 5634, 5636, 5645, 5784, 5912, 5999, 6119–6133, 6195, 6197, 6265, 6478, 6484–6488, 6527, 6530, 6620–6621, 6630
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	3261	209	94%

Tests	Skipped	Failures	Errors	Time
1689	48 💤	0 ❌	0 🔥	2m 12s ⏱️