Tuple Support for Headers

[eldonferranpol]

Intending to put in a pull request for headers to allow for the passing of tuples something along these lines:

request.WithHeaders(("Accept", "application/json"), ("host", "localhost"), ("etc", "etc"))

[tmenier]

(Pulling over some notes from #536.)

Need to evaluate what other areas might benefit from this. Possibilities:

• SetQueryParams
• WithHeaders
• WithCookies
• AddStringParts (multipart)
• Various things in HttpCallAssertion

Searching for ToKeyValuePairs is a good way to identify candidates. This doesn't necessarily mean it needs to be added everywhere. Not a breaking change so this doesn't need to get out for 3.0.

[tmenier]

Still like this idea but in the interest of time it won't make the initial 4.0 cut. Possibly 4.1.