Match application/json when Accept includes charset

[gyanu2507]

Accept: application/json;charset=utf-8 listed application/json from mediaTypes(), but mediaTypes(['application/json']) returned nothing because every Accept parameter had to exist on the provided type.

charset on Accept is not a type discriminator unless the provided type also names one. application/json;charset=utf-8 still matches application/json. Conflicting charsets (utf-8 vs iso-8859-1) do not match. text/html;level=1 vs text/html is unchanged.

profile on application/ld+json is a different parameter and is not in this change.

[kilisamemarisaaa]

I found two actionable issues at exact head e855534:

1. The fixes #62 claim is not satisfied. Issue #62's reproducer is Accept: application/ld+json;profile=http://www.w3.org/ns/json-ld#expanded with mediaType(['application/ld+json']); running this head still returns undefined because only charset is filtered and profile remains a required parameter. Please either remove fixes #62 or include the profile behavior and a regression test before claiming the issue is fixed.

2. Filtering charset for every media type changes parameter matching in a way that can select an unacceptable representation. At this head, Accept: text/plain;charset=utf-8 with provided ['text/plain;charset=iso-8859-1'] returns the ISO-8859-1 type. Media-range parameter semantics are media-type-specific; an unconditional filter cannot safely assume that every charset parameter is irrelevant. The existing discussion in #35 and the maintainer guidance in #41 also treat charset/other parameters as type-specific. Please retain parameter matching by default (or document and scope an explicit policy) and add a regression test for conflicting charset values.

[gyanu2507]

Both notes from the review are in c71457a.

fixes #62 is gone from the body. This PR only covers charset: Accept: application/json;charset=utf-8 still selects application/json, and Accept: text/plain;charset=utf-8 no longer selects text/plain;charset=iso-8859-1. Tests for both cases are in test/mediaType.js. profile is unchanged.