Add AUTHORS file

This will be picked up by npm. I used the output of this command:
git log --format='%aN <%aE>' | tail -r | perl -nle 'print $_ unless $a{$_}; $a{$_} //= 1;'
and manually tweaked a few things
Update build; Remove some unused variables
add function wrapper
Merge pull request #268 from NickQiZhu/anon_wrap

Add an authors files that will be picked up by npm. Wrap dc.js in an anonymous function. Remove some unused function params