renderdoc 0.7.0

Added

• Write more doc comments and add doc tests.

Changed

• Bump float-cmp dependency to 0.5.
• Switch to Circle CI Rust 1.33.0 image.
• Change error type of launch_replay_ui() from () to String.
• Mark Deref block as #[doc(hidden)] for cleaner generated docs.

Removed

• Remove internal renderdoc-derive crate in favor of declarative macro.
• Eliminate unnecessary unsafe blocks.

Fixed

• Define CaptureOption, InputButton, and OverlayBits in terms of
  renderdoc-sys types.
• Add missing discriminant values to InputButton enum.
• Fix broken Windows build (PR #61).