First pass at Windows installer

* vip-init.bat prompts for UAC and launches the powershell script
* vip-init.ps1 is the powershell script that sets everything up

When you double click a powershell script in Windows, it just opens in a
text editor. When you double click a .bat file it runs.
Pin WP-CLI to v0.12.0

Keeping WP-CLI on v0.12.0 so we always know what version we're on. We
can bump it manually in the future and fix  stuff that may break. Fixes
#13
Fix Vagrantfile

* There was some brokenness when we set the hostname.
* Maps the MySQL port locally
Update README with Windows instructions

The Windows installer works now, so we should update the README to
reflect that
Merge branch 'master' into windows

Conflicts:
	Vagrantfile
Merge branch 'windows' of https://github.com/Automattic/vip-quickstart into windows
Merge branch 'master' into windows
Merge branch 'master' into windows
Only run the SVN installer once
If SVN isn't installed, ask for a WordPress.com username and password
so we can offload the SVN checkout to the VM
Check for requirements on Windows

see #58
Sync vip-init bash script with vip-init powershell script
Merge branch 'windows'