Add create_dmd_release utility.

This is a tool to automatically generate both OS-specific and "all OSes" releases of DMD in both zip and 7z format, directly from the github sources.

The "how to" documentation is at the top of the source file:

https://github.com/Abscissa/installer/blob/create_dmd_release/create_dmd_release/create_dmd_release.d

NOTE: This tool "sort of" depends on itself actually being in the official repo. It will work fine before being pulled into the official repo, but the files in the "create_dmd_release/extras" won't be included in the releases it generates. Until this pull request gets merged, you can work around that like this:

After performing step #1 in the "Typical Usage" instructions at the top of the file (ie, extracting dmd-localextras.7z), then download the "create_dmd_release/extras" directory tree in this pull request. Merge both the "extras/all/dmd2" and "extras/[your os]/dmd2" trees into your "localextras-[your os]/dmd2" directory, and then proceed as normal.

I've tested this on the following platforms:

- Windows: Building both 32- and 64-bit on a Win7 64-bit machine.
- Linux 32-bit: Building --only-32 on a Debian 7 32-bit machine.
- Linux 64-bit: Building --only-64 on a Debian 6 64-bit (non-multilib) machine.
- FreeBSD 32-bit: Building --only-32 on a FreeBSD 9.1 32-bit machine.
- OSX: Building both 32- and 64-bit on an OSX 10.7 machine, however, that was a week ago so it's possible this tool could have had a regression from one of the changes I've made since.