glsh: introduce help command that lists scripts

This introduces a glsh help command, and defaults glsh to this command if no other args are set.

Before:

➜  ~ glsh

/usr/local/bin/glsh: line 12: $1: unbound variable

After:

➜  ~ glsh

create_kubernetes_rules.rb		help					update
delete_orphan_kubenetes_rules.sh	kube