If a specified version is not installed, use npm install to lazy-load the missing version.

Currently, only a few coffee-script versions are allowed.
Lazy-loading missing versions would allow any version to be used.

Also, users would no longer need to install multiple coffee-script versions when calling:
npm install -g coffee-build

Add the -m option to signal that sourcemaps should be created.

coffee-build src -o lib -m

This creates a .map file for every .coffee file, and saves it in the output directory.

Error: missing input path

This error will appear when you do the following:

coffee-build -o js src

Unfortunately, you must put the src first.

coffee-build src -o js