Plazy

Added APIs:
- plazy.setattr_from_dict(obj, kv, override=True)
- plazy.is_number(s)
- plazy.write_txt(path, lines, mode="w", cat_str="\n")

Modified APIs:
- plazy.read_txt(path, line_func=None, skip_empty_line=False)

Added APIs:

* plazy.b64encode(value, pretty=False)
* plazy.b64decode(value)
* plazy.unique(seq, sort=False, reverse=False)

Added APIs:
* plazy.read_txt(path)
* plazy.random_string(size=6, digit=True, lower=True, upper=True)

* Added **plazy.list_files**(root, filter_func=None, is_include_root=False).

* Auto assign