update ast-types and add regenerator-6to5
add File and Program to builder keys
fix up react display-name test whitespace
switch to regenerator-6to5
finalize ast-types
use file node builder and save parents to ast tree
remove _parent from nodes in traverse.removeProperties
use Program builder
only use needsParens if the node has changed parent
change Runtime to Optional runtime in README
only prepend whitespace to properties if we're the first