class Grape::API::Instance

def call(env)

(http://www.rubydoc.info/github/rack/rack/master/file/SPEC) for more.
the headers, and the body. See [the rack specification]
from Rack and ultimately returns an array of three values: the status,
This is the interface point between Rack and Grape; it accepts a request 
def call(env)
  compile!
  call!(env)
end