fix: add support for text/plain; charset=utf-8

[JKRhb]

This PR fixes #33. It adds support for the Content-Format text/plain; charset=utf-8 as an input parameter. The default output Content-Format will now be changed to text/plain; charset=utf-8 so this might actually be a breaking change. I hope, however, that other implementations will be able to handle this.

[JKRhb]

We might have to find a better way for dealing with content-formats which contain additional parameters in the future. At the moment, only the part before the first ; is being used. This approach, however, is not usable with new content-formats like application/cose; cose-type="cose-encrypt" or application/cose; cose-type="cose-mac" where the parameters actually contain important information.

[JKRhb]

@awwright: Would you still be interested in this issue?

[awwright]

I recall the reason I didn't was because it could break backwards compatibility in applications that use merely text/plain to refer to format 0. I'm not sure how much of a problem this actually is or a good way to fix it.

[JKRhb]

I recall the reason I didn't was because it could break backwards compatibility in applications that use merely text/plain to refer to format 0. I'm not sure how much of a problem this actually is or a good way to fix it.

Hmm, yeah, I am not so sure either. Maybe a more complex process (i. e. actually parsing the parameters) is needed to distinguish different content-formats, at least when they are given as an input. In any case, considering the potential breaking change it might be better to defer this PR to version 1.0.0.

[coveralls]

Pull Request Test Coverage Report for Build 1282106479

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.006%) to 89.828%

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Totals
Change from base Build 1280604248:	0.006%
Covered Lines:	1091
Relevant Lines:	1182

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💛 - Coveralls

[JKRhb]

I now opened and merged #282 which deals (partly) with the parameters issue. I am closing this PR for now but Content-Format 0 should probably be revisited in the future.