Bower install - add ability to specify an empty string in paths

To run `bower install`, for existing component.json

Also improve docs.
escape double %% opening tags with underscore templates
Don't throw on this.write() with empty string

Eg: `this.write('file.css', '');`
Apparently mocha.opts doesn't take since it still times out

@mklabs thoughts?
Changed broken link on line 18 of readme.md
Merge pull request #158 from timbo/generator-readme-linkfix

Changed broken link on line 18 of readme.md