ENH: Better report coverage

Sped up the BEM plotting a bit, and allowed setting the step. @mainakjas see what you think.
I see the following output

```sh
Embedding : jquery-1.10.2.min.js
Embedding : jquery-ui.min.js
Embedding : bootstrap.min.js
Embedding : jquery-ui.min.css
Embedding : bootstrap.min.css
```
Only the `_init_render()` function is verbose.