Small cleans.
The old way to clear the screen is too redundant. Pass a argument to
`clear` to decide if everything should be cleared.
Smarter way to set default prompt.
All strings are unicode in `help`.
Remove deprecated parameters.
Document.
Implemented a pseudo prompt which will be re-printed on `update`.
Bump to v0.1.1. Now ZhiGo will print out the prompt after each refresh.