option handling; more flexible CSS; README.md details

## jquery.timeselector.js:

### FIX: option handling
-- What: Picking directly ```arguments[i]``` (no error if not exists), merging it with defaults, attaching defaults
-- Why: Setting options as documented (see https://github.com/nicolaszhao/timeselector#options) made timeselector not work at all, unfortunately without an javascript error or something else
-- Note: I fear I didn't fully understand the original code at that place ... beg your pardon if mine's is rather primitive, but it works ...

### additional way for options
++ What: Adding a check for an INPUT element with ```name=*name of timeselector input*-timeselector-opts``` whose (unchecked!) VALUE will be applied as options (hours12 / step)
++ Why: In, e.g., a CMS you may have no access to the JavaScript part where you could set timeselector options via jQuery parameter, but to the HTML part where you could place an INPUT to store options for timeselector
++ Note: Imagine a CMS where timeselector is more generally invoked by ```class``` instead of ```name``` which would more easy allow for multiple timeselector inputs (provided a solution for (nicolaszhao#2) where you then can define an individual option input *in situ* of each timeselector input

## jquery.timeselector.css: binding styles to div for more flexibility
++ What: ```timeselector {``` => ```div.timeselector {```
++ Why: These styles are meant exclusively for the div that houses the + / - for time selection, making the deep connection to that div explicit allows using independent / more general ```timeselector``` class(es) (defined somewhere else), esp. giving the corresponding ```input``` element the class "timeselector" without being forced to state explicitly ```input.timeselector``` (which would make no sense if you want to say very general "this input belongs somehow to a timeselector context, details open" - but not (as for div.timeselector) "this input should behave in a very, very special way")
++ Note: changing to ```div.timeselector``` is "cheaper" than changing to something like "timeselector-div" which would require to change also the JS code
## README.md

### some detail on options hours12 and step
-- What: adding some detail to Usage and Options for ```step``` and stating ```hours12``` clearer
-- Why: ```step```: one might start with changing timeselector's by overseeing that setting a starting time in the HTML page does the job; ```hours12```: "whether or not to show AM/PM" does not describe it exactly

### only one timeselector per page
++ What: Adding section "Restrictions" to make prominent that you can only have one timeselector per page
++ Why: Beside reporting the stated fact as an issue it should be kept in mind for implementing timeselector for the time being

### JSON standard compliance in example
++ What: changing example JSON ```{hours12: false}``` to ```{"hours12": false}``` to comply with [The JSON Lexical Grammar](http://www.ecma-international.org/ecma-262/5.1/#sec-15.12.1.1)
++ Why: Copying the example without double quotes around the JSONString keyword (here: "hours12") to general JavaScript contexts will produce errors, see also [jQuery.parseJSON()](http://api.jquery.com/jquery.parsejson/)

### Adding additional way for options

see (https://github.com/hh-lohmann/timeselector/commit/3a9dd782ce87df041ecfe916df18b22386c84801)