v0.8.1 🪲 Fix model saving issues

We fixed two model-saving issues in some conditions:

1. unintended overwrite of the existing model file when calling func .save() even with arg overwrite default to False;
2. model_saving_strategy=best does not work and pypots still save every better model;

What's Changed

• Fix unintended overwrite saving by @WenjieDu in #516
• Update conda_dev_env.yml by @WenjieDu in #517
• Fix unintended overwrite when saving models and update conda dependencies by @WenjieDu in #518
• model_saving_strategy=best does not work by @WenjieDu in #514
• Update docs by @WenjieDu in #523
• Fix model saving issue and update docs by @WenjieDu in #524
• Fix error link to Reformer on openreview by @WenjieDu in #527
• Update docs and release v0.8.1 by @WenjieDu in #528

Full Changelog: v0.8...v0.8.1