Added definitions for JQuery plugin jSignature

Definitions for jSignature jQuery plugin including tests for
definitionss.

Included are some documentation on the typed definition functions making
use of JDocs TypeScript support.

Updated the readme to include the new Typed Definition.
Included empty tscparams files to be consistent with other definitions
in the project.
Merge pull request #1790 from pjmagee/master

Added definitions for JQuery plugin jSignature