0.20.4

Added

• Tuning parameters now (officially) exposed in the C API.

• futhark autotune is now 2-3x faster on many programs, as it now
  keeps the process running.

• Negative numeric literals are now allowed in case patterns.

Fixed

• futhark_context_config_set_profiling was missing for the c backend.

• Correct handling of nested entry points (#1478).

• Incorrect type information recorded when doing in-place lowering (#1481).