Nap should default accept header to `*/*`

[mstade]

Currently, nap sets the accept header to application/x.nap.view whenever it's not defined. This should change to set it to */* instead.

[mstade]

For resources with multiple representations, what heuristics should nap use to determine which representation to use? Whatever comes first? It probably makes sense to implement some sort of order, much like how browsers have default accept strings for requests – e.g. Chrome sends text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8.

[mstade]

Thinking about this some more it might be useful to prioritize text/html in the accept type, and make it trivial to implement a kind of options html resource that explains the interface of the resource. I think this could be a boon to discoverability, especially if combined with the thoughts in #8 and #22 with regards to registering and looking up resources using the same request mechanisms as anything else. Need some further thought to come up with ideas on what this might look like though.