Cachebox

Fixed
- Fix `TTLCache.__str__`
- Dependencies updated

Fixed
- Fix `BaseCacheImpl.__class_getitem__`
- Fix `cached` and `cachedmethod` typehint

Added
- New function `is_cached` is added.
- New parameter `callback` is added to `cached` and `cachedmethod`: now you can set a callback for cached functions.

Changed
- Some docstrings are changed.

Fixed
- [manual_inspect](https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect) warning fixed

Fixed
- `cached` and `cachedmethod` type hint fixed

Fixed
- fix https://github.com/awolverp/cachebox/issues/11

Fixed
- fix https://github.com/awolverp/cachebox/issues/10