Fixes #1. Inspect Accept header and return proper Content-Type.

[statonjr]

Returns Content-Type of 'vnd.collection+json' for API requests if client specifies 'Accept: vnd.collection+json'. Otherwise, send 'application/json'.

[mamund]

cool. looks good. I'll merge this in and publish over the weekend.

Thanks.

[johnlim]

Where do you submit an errata for this book? The book mentions

wget -S  -O - http://www.youtypeitwepostit.com/api/

should return Content-Type: application/vnd.collection+json but it does not.

$ wget -S --header "Accept: vnd.collection+json" -O - http://www.youtypeitwepostit.com/api/

also returns Content-Type: application/json
Why?