Improvements to the cli

[matthewp]

This adds a bunch of improvements to the cli like aliases for --config and --main, makes build the default command, package.json!npm the default config. Also adds some tests, which we didn't have before. Closes stealjs/steal#352

Changes

1. The flags --config and --main have been aliased to -c and -m respectively.
2. build is now the default command, meaning you don't have to specify steal-tools build every time.
3. By default the config is package.json!npm. This means if you're using the npm plugin you only need to type steal-tools to get a build going.
4. Options added for --source-maps and --source-maps-content to toggle on source maps behavior. See the documentation for what these mean.
5. Option --no-minify added to disable minification.

See all options available with steal-tools --help.

Examples

A normal build can now be:

steal-tools -c config.js -m app/app

Or if using the npm plugin it is just:

steal-tools

To create source maps add the flag:

steal-tools --source-maps