Use node-glob to recurse through files
Speed up asset generation by reusing compiled assets for non-hashed files.

before:

$ time ~/src/git/learnup/rails-source-maps/bin/rails-source-maps .
Generating source map for file: ./public/assets/admin.js
Generating source map for file: ./public/assets/admin-9666874371eb0c13889f55d8d369f6fd.js
Generating source map for file: ./public/assets/employers-3f85a5425d6eab3185a29b6202b0ddcb.js
Generating source map for file: ./public/assets/employers.js
Generating source map for file: ./public/assets/front_end-fcba15df371ce97b76a98b4b6aa1e10b.js
Generating source map for file: ./public/assets/front_end.js
Generating source map for file: ./public/assets/infobox-d3dbb779344892996c16a8d92949de49.js
Generating source map for file: ./public/assets/infobox.js
Generating source map for file: ./public/assets/js_only-39690accf50879cf9e16ce5d3a4638dc.js
Generating source map for file: ./public/assets/js_only.js
all files have been processed

real	0m50.849s
user	0m50.166s
sys	0m0.932s

after:

$ time ~/src/git/learnup/rails-source-maps/bin/rails-source-maps .
Generating source map for file: ./public/assets/admin-9666874371eb0c13889f55d8d369f6fd.js
Generating source map for file: ./public/assets/employers-3f85a5425d6eab3185a29b6202b0ddcb.js
Generating source map for file: ./public/assets/front_end-fcba15df371ce97b76a98b4b6aa1e10b.js
Generating source map for file: ./public/assets/infobox-d3dbb779344892996c16a8d92949de49.js
Generating source map for file: ./public/assets/js_only-39690accf50879cf9e16ce5d3a4638dc.js
Reusing source maps for file: ./public/assets/admin.js from file: ./public/assets/admin-9666874371eb0c13889f55d8d369f6fd.orig.js
Reusing source maps for file: ./public/assets/employers.js from file: ./public/assets/employers-3f85a5425d6eab3185a29b6202b0ddcb.orig.js
Reusing source maps for file: ./public/assets/front_end.js from file: ./public/assets/front_end-fcba15df371ce97b76a98b4b6aa1e10b.orig.js
Reusing source maps for file: ./public/assets/infobox.js from file: ./public/assets/infobox-d3dbb779344892996c16a8d92949de49.orig.js
Reusing source maps for file: ./public/assets/js_only.js from file: ./public/assets/js_only-39690accf50879cf9e16ce5d3a4638dc.orig.js
all files have been processed

real	0m28.842s
user	0m28.384s
sys	0m0.636s