Support for typescript generation
Currently, the only technologies I have knowledge of how to use on the web is javascript and typescript.

The only one that kaitai struct is able to compile into at the moment is javascript. While it's still significantly better than nothing, utilizing the generated javascript is difficult (or at least very tedious) compared to other programming languages.

I attribute this tedium to the lack of autocompletion that javascript offers. IDEs such as VSCode  are unable to provide "smart" autocompletion for javascript. However, it is able to do so for typescript. This removes the necessity to memorize every little part of the structure when writing code to work with the structures.

Here is an example of what I'm talking about with autocompletion: ![image](https://user-images.githubusercontent.com/3662774/54934400-d429b280-4ef4-11e9-96a9-12fe5bb632f3.png).

the suggestion "mainHeader" would not show up if this were created in plain javascript. However, because it's a snipped of something custom I developed in typescript, it shows up. This would significantly cut-down on the development time of web-based projects utilizing Kaitai Struct's generated code.

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**TL;DR:** 
- **GOAL**: 
to generate typescript code (or at least definitions)

- **HOW THIS WOULD HELP**:
It would cut down on development time of web applications utilizing Kaitai Struct.