Add CI badges to Cargo.toml

[kbknapp]

Cargo.toml publishes CI badges for tier 1 platforms (C-CI)

The Rust compiler regards tier 1 platforms as "guaranteed to work."
Specifically they will each satisfy the following requirements:

Official binary releases are provided for the platform.
Automated testing is set up to run tests for the platform.
Landing changes to the rust-lang/rust repository's master branch is gated on
tests passing.
Documentation for how to use and how to build the platform is available.

Stable, high-profile crates should meet the same level of rigor when it comes to
tier 1. To prove it, Cargo.toml should publish CI badges.

[badges]
travis-ci = { repository = "..." }
appveyor = { repository = "..." }

[mgeisler]

Fixed by 78498bd.

[kbknapp]

Thanks, forgot to close this 😉