ignore props.status in ctx.throw
docs: add ctx.headers alias
Merge pull request #333 from dead-horse/throw

ignore props.status in ctx.throw
make the second argument to throw properly optional
support errors and update docs
Merge pull request #334 from ianstormtaylor/add/throw-optional-status

Add/throw optional status
Release 0.10.0
bump vary and parseurl
dethroy -> destroy
finished -> on-finished

removes the writable test because it’s fake and there are tests for
on-finished for this case
bump on-finished
add fn assertion to app.use(). Closes #337