thcrap_configure: Add shortcuts to Steam library

[nmlgc]

Description

Quite a number of people have commented that integrating the thcrap shortcuts into Steam is a bit unintuitive. This point has become particularly relevant now that ZUN is investigating official download releases. In the future, Touhou games might very well be distributed through Steam, making a proper integration all the more desirable.

Prerequisites

None.

Implementation

You would think that Steam offers an API for managing the shortcuts to non-Steam applications. But no, you have to parse the Windows registry and manually write binary files to edit the shortcut list. The Ice project seems to be a "reference implementation" of how to achieve something like this - we'd only have to adapt its code.