* Allow max request size to be user-specified
This turned out to be way more impactful than I'd expected because I
felt like the right granularity was per-listener, since an org may want
to treat external clients differently from internal clients. It's pretty
straightforward though.
This also introduces actually using request contexts for values, which
so far we have not done (using our own logical.Request struct instead),
but this allows non-logical methods to still get this benefit.
* Switch to ioutil.ReadAll()
