Remove comments that don't fit our license

[Lokathor]

This should resolve #215

Per the latest comment on the issue, we just have to remove the comments, we don't have to actually change our rust code.

I've let stay:

• Comments indicating where the ported code came from, which naturally must have been written by someone doing the rust work.
• Comments that are a math expression without any English (which should be "a fact" and not copyright-able, i think).
• Comments that were obviously added by someone writing the Rust, such as FIXME/TODO, explanations of when we're trying to get LLVM to do the right thing, etc.

Also I've added a blank rustfml.toml which should ensure that the crate always uses the default format settings.

This should be ready for review. I may have removed too much or too little of the comments, but there should be no code changes.

[BartMassey]

Rather than this, I would prefer to see #241 resolved as suggested by @joshtriplett there: put the original copyright notices back.

[joshtriplett]

We should not be trying to delete comments in order to get out of preserving copyright notices. We should just preserve the copyright notices, and put them in the COPYRIGHT file.