context req; pre-parsed body

[chilltemp]

• Add the req: HttpRequest object to the context function so that context creation has access to the raw request. Use case: custom auth needs the request headers
• body parsing: v0.1.1 broke our implementation because it expected body to be a string, yet ours was already JSON.parse'd. The code now only parses when necessary.

[trevor-scheer]

Hey @chilltemp, this fix was already implemented in #35, but if you'd like to rebase this PR and repurpose it for adding req to context that seems reasonable!

[chilltemp]

Done, thanks! See #40