JsonUtils.fromURL() delegates to DocumentLoader.fromURL()
unused private method resolve() removed
DocumentLoader methods made non-static

.. so that it makes sense to provide a DocumentLoader to
JsonLdOptions - e.g. one can customize http client just for one
parsing session.

WARNIG: This will break backwards-compatibility with v0.3
Moved out DocumentLoaderTests from JsonUtilsTest
Use JAR cache
test jarcache, through thread contextloader
Embedding JarCacheStorage

Originally conceived at https://github.com/myGrid/httpclient-jarcache
by Stian Soiland-Reyes (me)
Test JarCacheStorage
Use shared httpClient unless explicitly set
README about HTTP client and JAR cache
README typos
Reformat to our style

Also rename TestJarCache to JarCacheTest for consistency
Merge branch 'jarcache'

Conflicts:
	core/src/test/java/com/github/jsonldjava/utils/JsonUtilsTest.java