Use component-installer rather than riding on component's private API

This allows us to (more easily) stay current with component's
installation processes and reduces our dependency footprint. :)

Closes #1.
Add default behavior to component-shrinkwrap(1)

Allows us to use the binary without specifying `--save` or `--install`.
If the component-shrinkwrap.json file is present, we'll install the
listed components.  Otherwise, if the component directory is present,
we'll build the component-shrinkwrap.json.

This does not change the existing API, just adds some sugar around it.
Merge branch 'pr/2'
update usage info in Readme
Merge branch 'pr/3'
Release 0.2.0