Update facebook.js

- adding support for data-width, default to 250 if it's not specified
- fixing errors
- adding link documentation
I guess `!!share` and `share || 'true'` should have same effect, isn't it? While I think `!!share` is more readable. Did I miss anything here?
As a reminder parameter must be provided as `false` not `'false'` as string since string will be considered as true always.

     <facebook-like share=false /> 

should do the job.