Token-based HTTP Authentication

Would you accept a pull request for http token authorization in unirest? It's handy in one of our projects and it seems like something that might be useful upstream (http header authorization tokens, not oauth.)

The issue names no files or tests. Start by tracing the Unirest Ruby request API and its existing authentication options, then determine how an HTTP Authorization token should be configured and sent without OAuth. Done means token authorization is supported with documented behavior and coverage for the resulting request header.

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