Expose recast.prettyPrint as a boring alternative to recast.print.

This method exists mostly so that I can contrast it with recast.print in README.md. The whole point of Recast is to make possible the magic of recast.print, so recast.prettyPrint is much less exciting.
Document the require("recast").parse and .print interfaces in README.md

Closes #27.
Bump NPM version to 0.4.1 in preparation for publishing.
Drop support for node v0.6, after too many spurious test timeouts.