Release 0.5.1

Note: The publish action jobs got some issue when publishing v0.5.0. PYPI won't allow you to re-publish your Python wheels with the same name even if you removed the released files, so have to fix this and re-publish as v0.5.1

What's new?

Features:

• Construction methods for List: repeat, arange and cycle;
• Rename from_iter function to from_seq, because it actually cannot handle iterable objects such as set, iter(obj) or mapObject;
• Does not support Python 3.6 any more.

Misc:

• Github action to publish ulist;
• Github action to build ulist documentation;
• Run CI for Python 3.7, 3.8, 3.9 and 3.10, instead of for Python 3.6;
• Auto generate doc by sphinx and publish documents to Github pages;
• Some updates in Readme.md;
• Further improve documents.