Chanfig

Commits
- 9d77060: make FlatDict not defaultdict (Zhiyuan Chen)
- e45cfaa: disable pycodestyle and enable pylint (Zhiyuan Chen)

Commits
- e4a41b3: add BSD-4-Clause license (Zhiyuan Chen)
- 3e75eb5: fix exception when infer arguments (Zhiyuan Chen)

Commits
- 7e8d6b4: improve Exception for getting/setting NestedDict (Zhiyuan Chen)
- 162a8e5: correct typo of unwraped (Zhiyuan Chen)
- 3c8da0c: switch to mkdocs-stable (Zhiyuan Chen)
- 8d6694c: add registry to chanfig (Zhiyuan Chen)

Commits
- bdfc185: fix default value overrides dict member (Zhiyuan Chen)

Commits
- bc9a369: add getitem and getattr for null (Zhiyuan Chen)
- be516aa: fix chanfig.difference (Zhiyuan Chen)

Commits
- fa39116: fix TypeError when children of ND is not ND (Zhiyuan Chen)