Make README.md consistent with recently cleaned-up package interface.
Make README.md consistent with recently cleaned-up package interface.

Commit 35907ae5b3048461a01ecefd0755c56820e09faa removed recast.namedTypes
and .builders in favor of recast.types.namedTypes and .types.builders.

ipeychev/recast,marcioj/recast,benjamn/recast,kyldvs/recast,benjamn/recast,rwaldron/recast,stefanpenner/recast,cpojer/recast,kassens/recast,ersengultepe/recast,benjamn/recast,fkling/recast,shumov/recast