feat(theme/mkdocs): add autofocus for search input when modal opens
feat(theme/mkdocs): add autofocus for search input when modal opens

After clicking the `Search` link, the search input in modal should be
autoselected for easier input.

> Due to how HTML5 defines its semantics, the autofocus HTML attribute has no effect in Bootstrap modals. To achieve the same effect, use some custom JavaScript:

```
$('#myModal').on('shown.bs.modal', function () {
  $('#myInput').focus()
})
```

__Ref:__
http://getbootstrap.com/javascript/#modals

williamjmorenor/mkdocs,tedmiston/mkdocs,fujita-shintaro/mkdocs,pjbull/mkdocs,gregelin/mkdocs,ramramps/mkdocs,simonfork/mkdocs,williamjmorenor/mkdocs,nicoddemus/mkdocs,nicoddemus/mkdocs,fujita-shintaro/mkdocs,waylan/mkdocs,vi4m/mkdocs,hhg2288/mkdocs,rickpeters/mkdocs,peter1000/mkdocs,samhatfield/mkdocs,d0ugal/mkdocs,cnbin/mkdocs,hhg2288/mkdocs,lukfor/mkdocs,dmehra/mkdocs,mkdocs/mkdocs,jimporter/mkdocs,mlzummo/mkdocs,dmehra/mkdocs,justinkinney/mkdocs,ramramps/mkdocs,samuelcolvin/mkdocs,longjl/mkdocs,pjbull/mkdocs,davidgillies/mkdocs,ramramps/mkdocs,samhatfield/mkdocs,simonfork/mkdocs,cnbin/mkdocs,rickpeters/mkdocs,jeoygin/mkdocs,samuelcolvin/mkdocs,d0ugal/mkdocs,simonfork/mkdocs,jimporter/mkdocs,lbenet/mkdocs,longjl/mkdocs,kubikusrubikus/mkdocs,williamjmorenor/mkdocs,nicoddemus/mkdocs,michaelmcandrew/mkdocs,davidgillies/mkdocs,mlzummo/mkdocs,hhg2288/mkdocs,waylan/mkdocs,tedmiston/mkdocs,lbenet/mkdocs,jamesbeebop/mkdocs,gregelin/mkdocs,lbenet/mkdocs,gregelin/mkdocs,jamesbeebop/mkdocs,lukfor/mkdocs,lukfor/mkdocs,kubikusrubikus/mkdocs,fujita-shintaro/mkdocs,samhatfield/mkdocs,waylan/mkdocs,justinkinney/mkdocs,rickpeters/mkdocs,jeoygin/mkdocs,mkdocs/mkdocs,tedmiston/mkdocs,michaelmcandrew/mkdocs,longjl/mkdocs,mlzummo/mkdocs,peter1000/mkdocs,dmehra/mkdocs,pjbull/mkdocs,michaelmcandrew/mkdocs,mkdocs/mkdocs,vi4m/mkdocs,peter1000/mkdocs,jimporter/mkdocs,jamesbeebop/mkdocs,samuelcolvin/mkdocs,cnbin/mkdocs,kubikusrubikus/mkdocs,vi4m/mkdocs,justinkinney/mkdocs,jeoygin/mkdocs,d0ugal/mkdocs,davidgillies/mkdocs