serve sourcemap from separate url

Allows for the serving of a sourcemap in production for a browser that
might request it. It is up to the user to enable sourcemaps with debug
option and to limit access to the sourcemap as they see fit.
add test for sourcemaps
drop support for node 0.8

Hand is forced by browserify :/
update uglify dependency
add sourcemap notes to readme
add 0.7.0 notes to changelog
add browserify note to changelog
0.7.0