Changes from the previous release: ([diff](https://github.com/alphatwirl/atpbar/compare/v0.9.2...v0.9.3))
- fixed the problem of returning from the outermost `atpbar` in the single thread. This problem was causing, for example, the command prompt to already have appeared while the progress bars were still growing in the interactive mode.
- added a new function `flush()`, which returns after the progress bars finished updating -- useful for threading and multiprocessing