Created a no-dependency script to bootstrap Windows DMD.

While this pull is just for Windows, a Posix version is in the works.

This is a one-file tool that has *no* prerequisites other than an internet connection and a working Windows machine (XP and up - untested on 2k). It will use Git if it's detected, but does not require it. The only other dependencies (DMC and a command-line unzip) are automatically downloaded by this script (but not installed system-wide, just placed in a subdirectory).

One nice effect of the above is that, if this pull is merged, any internet-connected Windows user who has [wget](http://gnuwin32.sourceforge.net/packages/wget.htm) installed can go from having *no* DMD whatsoever to a basic bootstrapped DMD with nothing more than one command:

```
wget https://raw.github.com/D-Programming-Language/installer/master/bootstrap/bootstrap-dmd.bat && bootstrap-dmd
```

(However, this script does *not* require wget or curl.)

This script is *deliberately* limited to building and setting up nothing more than Win32 DMD, Druntime, Phobos and RDMD. My intention is with that much bootstrapped by this batch file, any further tasks can be implemented *in* D.

I tested this on WinXP 32-bit and Win7 64-bit, and also from arbitrary directories (it not just the directory with the script), and inside paths containing spaces.