Remove lib/resolver.js.

The Resolver functionality has been replaced by
BuildContext.prototype.findDirectiveP and require("brigade").source.
Cache built modules in <outputDir>/.modules-cache/<hash>.js

This makes the total build time proportional to the number of modules that
need to be re-built.
Display colorful progress.

These messages go to STDERR so that they can be differentiated from the
JSON tree output.

Still, it might be good to allow this output to be silenced with a --quiet
flag or similar.