Provide utility functions without requiring a target .sol file

[tbrent]

It doesn't really make sense that you need to specify a .sol file in order to use show-eth, send-eth, code-at, or show-gas, or address. Unfortunately the currently design requires this.

We should provide these as top-level commands instead. When we do this, we should also move the --license flag out and make it one of these top-level commands as well.