Cygwin setup improvements

Combined the best bits of the improvements suggested by
Ross Smith II <ross@smithii.com> and Joe Fitzgerald <joe.fitzgerald@emc.com>
(via https://github.com/joefitzgerald/packer-windows):

Changelog:

- Removed package dependencies, as Cygwin setup 2.830 no longer requires them to be listed.
- Changed mirror to http://mirrors.kernel.org/sourceware/cygwin/ for speed.
- Replaced hardcoded C: drive references with %SYSTEMDRIVE%.
- Hardcoded architecture to "x86" as "x86_64" seems a bit buggy still, except
  for Windows 2012/2012R2 templates on which 32-bit version seems to crash
  a lot)
- Use Powershell extensions instead of the now deprecated bitsadmin to download remote files
- Changed temporary directory from C:\WINDOWS\temp to %TEMP%.
- Added additional comments
- Split monolithic postinstall script into smaller, more reusable .BAT scripts (which are more appropriate to the Windows platform than Unix-style .sh shell scripts)

Tested these changes, and the boxes

````
win2008r2-datacenter
win2008r2-enterprise
win2008r2-standard
win2008r2-web
win2012-datacenter
win2012-stnadard
win2012r2-datacenter
win2012r2-standard
win7x64-enterprise
win7x64-pro
win7x86-enterprise
win7x86-pro
win81x64-enterprise
win81x64-pro
win8x64-enterprise
win8x86-enterprise
````

successfully install OpenSSH, and VMWare Tools.
Symlink Ruby 1.8 to 2.0.0
Permit optional install of chef-client.

The default is still to not install chef-client and assume that
the vagrant-omnibus installer will be used to install chef-client, but
if you set the user variable chef_client with the version of chef-client
desired, it will install chef-client.
Example: packer build -var 'chef_version=11.8.0-1' win2012r2-standard.json
Permit optional install of chef-client - Windows

The default is still to not install chef-client and assume that
the vagrant-omnibus installer will be used to install chef-client, but
if you set the user variable chef_client with the version of chef-client
desired, it will install chef-client.
Example: packer build -var 'chef_version=11.8.0' win2012r2-standard.json
Deleting netboot version of centos510, will be solving this issue a different way
Fixing 32-bit CentOS templates to use a 32-bit guest os type
Per Brian Flad <bflad417@gmail.com>, switching chef_version toggle to be
provisioner/provisioner_version:

* Add provisioner variable and PROVISIONER environment variable
* Rename chef_version variable to provisioner_version
* Rename CHEF_VERSION environment variable to PROVISIONER_VERSION
* Rename chef.bat script to provisioner.bat
* Use PROVISIONER to determine action in provisioner.bat
Deleting old chef.bat files left behind
Fixing typo in user variable macro reference
Adding provisioner toggle to CentOS templates:

Per Brian Flad <bflad417@gmail.com>

    * Add provisioner variable and PROVISIONER environment variable to
      determine provisioner type
    * Add provisioner_version variable and PROVISIONER_VERSION variable to
      specify provisioner version
    * Use PROVISIONER to determine action in provisioner.sh
Adding provisioner toggle to Ubuntu templates:

    Per Brian Flad <bflad417@gmail.com>

        * Add provisioner variable and PROVISIONER environment variable to
          determine provisioner type
        * Add provisioner_version variable and PROVISIONER_VERSION variable to
          specify provisioner version
        * Use PROVISIONER to determine action in provisioner.sh
Fix Windows 8.1 guest_os_type for x86 template
Adding WinRM-compatible win2012r2 image for use with vagrant-windows
Fix missing TEMP and TMP environment variables

Changelog:
- All windows templates: Added `TEMP` and `TMP` variables as Cygwin doesn't pass them to `cmd`
- All windows scripts: Changed `%LOCAL_TEMP%` to `%TEMP%` now that it's properly initialized
- All windows templates: Fixed `USERNAME` variable as Cygwin sets this to `cyg_server`
- All windows templates: Changed `C:/cygwin/tmp/script.bat` to `$(/bin/cygpath -m '{{.Path}}')`
- All `vagrant.bat`s: Use `%USERPROFILE%` as it's always available
- All `vmtools.bat`s: Standardized (use `if exist "%SystemDrive%\Program Files (x86)"` throughout)
- All `vmtools.bat`s: Delete all downloads after use
- All `vmtools.bat`s: Quoted paths, as appropriate
- All `.bat` files: Removed `endlocal`s, as it's implied (see `SETLOCAL /?`)
Fixing EnableDelayedExpansion issues
Adding Windows 8.1 WinRM templates (and updating Windows 2012R2 scripts to match)
Based on the work Joe Fitzgerald has done in https://github.com/joefitzgerald/packer-windows and contributions from Dylan Meissner <dylanmei@gmail.com> added basebox templates for Windows Server 2012R2, Windows Server 2012, Windows Server 2008R2, Windows 8.1, Windows 8 and Windows 7
Added some new VMWare Fusion 6.0.2/VMware Workstation 10.0.1/VirtualBox 4.3.2
baseboxes to the README.md.  Also added updated instructions for the new
"provisioner" & "provisioner_version" user variables and Windows template
instructions.
Deleting the old Windows README
Adding provisioner toggle to Debian templates:

    Per Brian Flad <bflad417@gmail.com>

        * Add provisioner variable and PROVISIONER environment variable to
          determine provisioner type
        * Add provisioner_version variable and PROVISIONER_VERSION variable to
          specify provisioner version
        * Use PROVISIONER to determine action in provisioner.sh