Unified Installer Script

* One installer script can be used to make an installer on 32- or 64-bit
Windows.
* If you're using 64-bit Windows, you can make a 32-bit or a
32-and-64-bit installer.
Delete Accessibility_Toolbar_x64.iss
Update Web-Accessibility-Toolbar.iss
Clean up README; Consistencyify install dir
Update Web-Accessibility-Toolbar.iss
Fix errant substitution.
Installer file

* More consistent variable naming
* Ensure only 32-bit files are included in the 32-bit install
* Improve comments
Add friendly warning to prevent version-thrashing.
Merge pull request #38 from ThePacielloGroup/matatk-installation

Single ISS File