Fix exception being caused by use of `public_send` in add_breadcrumb macro
Don't attempt to display a flash message if the message can't self-convert to a string.

- Example: `flash[:notice] = true`. There's no point displaying this flash message in the page. Even if we did explicitly convert it to `"true"` that wouldn't be a useful message.
Merge pull request #8 from pdobb/bootstrap-3.0.0

bootstrap_flash and add_breadcrumb fixes