Merge pull request #88 from nevir/jshint

Stupid basic jshint check in npm test
Document CLI options and arguments for --help.
BREAKING CHANGE: yo polymer:seed now requires an element-name argument.

This allows us to construct the element's directory and be a _litte_ bit
more safe about the .bowerrc madness.
Warn the user if they are attempting to generate a seed element in
what appears to be an unsafe workspace.