Add more baselines.

[zezhishao]

General Time Series Forecasting:

• DeepAR
• LightGBM
• NBeats
• NHiTS ✅
• GRU

Spatial-Temporal Forecasting:

• STGODE ✅
• STSGCN❌, STFGCN❌ (They are built on MXNet)
• SCINet

Long Time Series Forecasting:

• TimesNet
• Vanilla Transformer
• GPTs for Time Series

[zezhishao]

TODO:

• 优化standard_transform，将scaler和参数存储的过程给重构一下。

[zezhishao]

Use AutoML to tune the hyper-params.

[zezhishao]

Add some how-tos:

• How to add new datasets.
• How to config the config file.
• How to inference and save the inference results.
• How to customize loss function.