Ensure 0 previous rows are removed when calling refresh on a freshly
created State. Before, 0+ rows were removed on an initial State
refresh. If the prompt had a newline in it, a positive number of rows
were removed, clearing past output in stdout.

Fix #109

Oops

Not tested

Only displayed on unix terminal.
For windows, we will have to remove ANSI escape sequence when
there is no support for ANSI colors (Windows < 10).

Completer::complete takes a mutable reference.
Editor takes a Option<Rc<RefCell<Completer>>.

Breaking change: by default, iterator does not add automatically
to history anymore.

Alternative to PR #120

Add Cargo category and badges

Add ability to get constant reference to history from Editor

Don't preserve history on the gh-pages branch when pushing latest documentation

Vi mode (#94)

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