v1.5.6

hmer 1.5.6

Major changes

• New functionality: diagnostic_pass for automated diagnostics and modifications of
  emulators; hit_by_wave for visualisation of history matching progress.

Bug fixes

• Fixed issue in simulator_plot et al. where some combinations of wave_numbers
  and zero_in caused out-of-index errors.
• Edge case fixes for training individual variance emulators or one-dimensional
  variance emulators.

Enhancements

• Vastly improved efficiency of emulator training when emulator_type = "variance" or
  emulator_type = "covariance".
• Improvement to hyperparameter estimation when training covariance emulators.