Added TypeScript declaration file and configuration

[Aryan-mor]

This pull request adds a TypeScript declaration file (ical.js.d.ts) for ical.js to enable TypeScript code to be used with ical.js. A tsconfig.json file has also been included to provide TypeScript configuration for the library.

The ical.js.d.ts file contains type definitions for the Component and Event classes and their associated methods, as well as the parse function.

In addition, the tsconfig.json file sets up the TypeScript compiler options required to transpile TypeScript files to JavaScript.

This change will make it easy to use ical.js with TypeScript and provide better type-checking and code completion in editors.

[kewisch]

I'd prefer not to take a manual approach here, since we'd need to maintain two separate file signatures. I'm ok adding some automation that would generate the d.ts from jsdoc, as noted in #367 (comment) . I appreciate you made the effort to send a PR, if you'd like to work out automation based on the jsdoc I'm all for it!