New Features

============

- Add `-invariant=off` option (dlang#6347)

  This option will inhibit emitting implicit invariant calls no matter if
  `-release` is used or not.

  This is done because invariants are not a pay-for-what-you use feature, even
  if you don't write a single invariant, for every public method call 2 new
  virtual calls will be done, which is a big overhead for an unused feature,
  even in non-release builds.

  Invariants can be still called explicitly in non-release move via
  `assert(this)`.