Implement tab completion

[alextsui05]

Hitting tab should fill the console with potential autocompletions like the interactive python interpreter does if you have it set up to do so.

[alextsui05]

This can be implemented using an rlcompleter.Completer. Call complete with a partial string and int n to get the n-th possible completion. Sometimes there's only one, in which case just complete it. Sometimes there's more, so gather it in a list and format it neatly as a message to print to the console.

[alextsui05]

Pressing tab should autocomplete with the largest common substring of all the current suggestions. In the case where there is only one suggestion, it completes the whole thing.