Mini-pole

Add more examples.

1. The code can now be installed via "pip install mini_pole" or "python3 setup.py install".
2. Fix several stability issues.

Minimal pole method for analytically continuing matrix-valued imaginary frequency correlation functions to the real axis, enabling precise access to off-diagonal elements and thus improving the interpretation of self-energies and susceptibilities in quantum simulation.

**Full Changelog**: https://github.com/Green-Phys/MiniPole/commits/v0.1