message: Documented the relocation module
diff: +//! The relocation package provide two structures: RelocSink, TrapSink.
  +//! This structures are used by Cranelift when compiling functions to mark
  +//! any other calls that this function is doing, so we can "patch" the
  +//! function addrs in runtime with the functions we need.
  use cranelift_codegen::binemit;
  use cranelift_codegen::ir::{self, ExternalName, SourceLoc, TrapCode};
  