Checking if selector matched to avoid initialization on undefined.
Renaming slides variable

Better call this slideables (plural) as it may contain more than one
ul, which is intended behaviour.
Initialising plugin differently.

Using a loop and a generally better approach on initialisation while
ditching unnecessary sliderWrapper param/default/variable.
No need for sliderWrapper anymore, just initialise on wrapper div.
Removing default params from initialisation.
Merge pull request #2 from TrueniTo/validation-and-refactor

Validation and refactor