Gsbg

Make fetch_selected_element_from_page() available for users.

**Full Changelog**: https://github.com/WenjieDu/Google_Scholar_Badge_Generator/compare/v0.1.2...v0.1.3

In this release, I made the following changes:

1. use logging to help print logs with timestamps;
2. rename the env variable `APPLY_MIRROR_SITE` to `APPLY_MIRROR_SITES`;
3. correct the error homepage links in `setup.py` so that the project on PyPI can link correctly with source code on GitHub;

I loose the criteria of the article citation selector in this version.