Completion function for gem-cd and gem-open.

@param [String] so_far what the user‘s typed so far @return [Array<String>] completions

Installs a gem with all its dependencies.

@param [String] name @return [void]

List gems matching a pattern.

@param [Regexp] pattern @return [Array<Gem::Specification>]

Get the gem spec object for the given gem name.

@param [String] name @return [Gem::Specification]