Add docs for event params
Add docs for event params

Add documentation for the parameters passed to `awesomplete-highlight`,
`awesomplete-select`, and `awesomplete-selectcomplete` event listeners.

bsvobodny/awesomplete,LeaVerou/awesomplete,bsvobodny/awesomplete,eggpi/awesomplete,bchcheng/awesomplete,LeaVerou/awesomplete,eggpi/awesomplete,bchcheng/awesomplete