Allow multiple arguments to API pack function

[danderson00]

Objects passed will be merged. This enables configurations like:

var sources = { include: '*.js', first: 'setup.js', last: 'api.js' };

pack(sources, { to: 'output.js' });
pack(sources, { to: 'output.min.js', minify: true });
pack(sources, { to: 'output.debug.js', template: 'debug' });