Add grunt task runner support (including minification)

[ericdahl]

I'm not sure what build system you prefer... but if Grunt is fine, then this pull request might be of use.

This pull request:

• sets up a basic Gruntfile
  • the most immediate benefit is having a dist/arc.min.js minified version (4.1 KB vs 9.1 KB)
  • includes jshint/tape testing support

[springmeyer]

I would prefer browserify + a simple makefile over grunt like https://github.com/mapbox/leaflet-omnivore/blob/master/Makefile or https://github.com/mapbox/geojson.io/blob/gh-pages/Makefile or

[ericdahl]

fair enough; that looks like a good solution as well

I appreciate the quick response.