Adding N-HiTS network (N-BEATS successor)

Added

• Added new N-HiTS network that has consistently beaten N-BEATS (#890)
• Allow using torchmetrics as loss metrics (#776)
• Enable fitting EncoderNormalizer() with limited data history using max_length argument (#782)
• More flexible MultiEmbedding() with convenience output_size and input_size properties (#829)
• Fix concatentation of attention (#902)

Fixed

• Fix pip install via github (#798)

Contributors

• jdb78
• christy
• lukemerrick
• Seon82