Add build without 3rd party libs
This build expects to find Underscore and Bean libraries as globals by
the time it is loaded. This is very useful for those how want to take
greater control of the libraries used.

Using this build RequireJS and Browserify users can manually setup a
shim configs for Flotr2.
Merge pull request #225 from epeli/nolibs

Add build without 3rd party libs
Merge remote-tracking branch 'flotr2/master'