add direct download links to the clang-format binaries

As a convenience, I'm hosting direct links to the clang-format binaries on my Digital Ocean server. The files are only 1-2 MB, and I have 1 TB of transfer per month, so that's plenty. Downloading a 1.3 MB file is better than downloading the entire ~58 MB toolchain, and it skips the extraction step. I'll update the links for every LLVM release. Feel free to re-word anything if you don't like it.

I also tested your plugin with the LLVM 3.5 version of clang-format on C, C++, and JavaScript files and had no issues. Your plugin works great!