message: add camd feature description
diff: +//! FFI bindings to the SuiteSparse component CAMD
  +//!
  +//! For a static build activate the "static" feature, which builds CAMD
  +//! from source and includes this statically.
  #[cfg(target_os = "windows")]
  pub type SuiteSparseLong = libc::c_longlong;
  #[cfg(not(target_os = "windows"))]
  