Implements command tab completion by leveraging the shell's built in completion features. Currently only bash is supported, but fish and zsh can/will be added in another PR. Command and option names are supported out of the box. Option/argument values can be defined by using the new suggested_values option when adding arguments/options which accepts either an Enumerable(String) or a block that should return an Array(String) if additional filtering is desired. The #complete method may also be overridden for more complex usages.

This functionality does require sourcing/placing a generated file in a location where you shell is able to read it. E.g. sourced within ~/.bashrc or placed within /etc/bash_completion.d/. This is a one-time setup, so not too big of a deal.

This can be done via the completion command that is bundled in with all console applications. E.g. ./console completion > completion.sh. Run ./console help completion formore information.

The name of the binary used to generate the script is important. In this case, completion.sh would handle auto completion for a binary called console, but not one called something else.

The completion script also is required to run with real binaries, not via like crystal run src/console.cr -- completion.

• Support tab completion
• Add helper assert_command_is_successful to the *Tester types

Resolves #293