Bump version: 0.2.0 → 0.3.0

chore: clean notebooks, ignore checkpoints; relax Python/NumPy versions

  - remove stray notebooks and .ipynb_checkpoints from repo
  - add .ipynb_checkpoints/ to .gitignore
  - delete unused modules: graphglue/adapters/corneto.py,  graphglue/core/adapter.py
  - lower NumPy minimum to >=2.2.6
  - no functional code changes

moved API_demo_notebook under docs

moved API_demo_notebook under docs