Refactored jQuery UI datepicker overloads and added JSDoc. Options still
to do - will follow in a later commit I hope. Removed unused
optionLiteral datepicker overloads (undocumented). Made the following
change to the underlying methodName overload to allow other overloads to
"chain" into it.
```
datepicker(methodName: string, ...otherParams: any[]): any;
```
Moved datepicker tests to single function. Added tests for datepicker
methods.
Very much just first steps. A lot to do in jQuery UI I think...
This enables each definition to have a readme if necessary.
Also a .json metadata file to help with package managers.
And last, to have different versions of the definitions.
