0.21.7

Added

• futhark check-syntax: check syntactic validity of a program
  file, without type-checking.

• Parsing multi-file programs is now parallelised, making it
  slightly faster.

• Reloading a large program in futhark repl is now faster, as long
  as not too many of its files have been modified (#1597).

Fixed

• Mistake in occurs check could cause infinite loop in type checker
  for programs with type errors (#1599).