add keygrip support

this.originalUrl && this.request.originalUrl

just realized this since we removed the top closure. i'm not sure if
there's a better way to sol...

Expose proto

until we figure out a good way to return both weak and strong validators

response.etag and response.lastModified

need tests for this

Add/ctx request response

correct the link

specifically 3xx codes except for 304. closes #66

replace content-negotiation accessors with 0-arity method calls

less common than .auth which we removed as well but we can
add them back if it becomes a common ...

pass an optional `next` to app.callback()

i'm not sure if this is incorrect. people should use `accepts()`
anyways.

pretty annoying to continuously update these. we'll start pining them
when you can actually use ...

get away from promoting the extension of prototypes, aside
from it looking better there isnt rea...

debug context: notify if a property is being overwritten

for node

i like keeping things as similar to node as possible :)

since it cant be anything else, but if you have middleware that transforms
the object to xml or ...

set length on body override

bind .onerror to context

onerror: check existence of error

this prevents a bunch of redundant checks that middleware may need to
check response length, typ...

Fixed typo

`ctx.accept` -> `ctx.accepts`

so you can easily unwind the stack for 404s

meaning the application could respond with this message if it likes

always has clientError now