0.35.0

CHANGES:

• Allow use of effect syntax in preprocessed files without causing migration
  failures. (#552, @hhugo, @NathanReb)

• Remove support for compilers older than 4.08 (#556, @NathanReb)

• Add a --use-compiler-pp flag to the standalone driver. This flag
  can be set when the driver outputs source code to make it use the compiler's
  Pprintast instead of ppxlib's.
  (#555, @NathanReb)