Switched Mac Downloads to the 32-bit; added 64-bit link; cleaning

Fixes #919:

* [x] switch Mac buttons from 64-bit to 32-bit (both the Bundle and SDK link)
* [x] add a **Note:** about grabbing the 64-bit versions if you wish:
![64-bit-mac-link](https://cloud.githubusercontent.com/assets/103167/4072439/0f3edc18-2e86-11e4-8a6b-cfbb82f224a9.png)
![64-bit-mac-sdk-link](https://cloud.githubusercontent.com/assets/103167/4072440/13f32052-2e86-11e4-9ee5-4c4097a2d450.png)


* [x] switch duplicated button code to use includes, passing in the bits (32 or 64) and arch (ia32 or x64)
* [x] newline the `<a>` tags in those buttons so that they didnt go a million miles off the edtior.
* [x] add the `download-link` class to 64-bit Linux and Windows Bundle links
* [x] fix the SDK `data-bits` (they all just said "32")
* [x] Title-Cased the buttons since they have `text-transform: uppercase` in their CSS now.

I hope we haven't been... using those download analytics because of the above issues. Since presumably that data is all garbage so far, I'd like to change the data-bits from "32" or "64" to be "ia32" or "x64", which would remove one variable from the button includes. Eh?

@kwalrath what do you think of the Note text? I borrowed it from @sethladd's comment.