v0.8.3

Thanks to @itslukej and #8 for the entirety of this release.

Additions

• Per-request authorization headers
• Construction with optional token
• Token provided in options rather than as a separate string
• Add missing Basic token type
• Rest.hasHeader added to check if a request has a header

Fixes

• Content-Type header conflicts for form data request payloads are now normalized to Title Case form