Ecstasy Development Kit (XDK) downloads

Download and install the latest XDK build:

Add a "tap" to access the XDK CI builds, and install the latest XDK CI build:

       brew tap xtclang/xvm && brew install xdk-latest

After doing steps 1 and 2, you can upgrade to the latest XDK CI build at any time:
```
       brew update && brew upgrade xdk-latest
```