message: Add cargo keywords and categories.
  Resolves Suggestions welcome for better keywords/categories, though there is a limit of 5 of each.
diff: @@ -3,7 +3,8 @@ authors = ["The Rust Project Developers"]
  description = "A collection of numeric types and traits for Rust, including bigint,\ncomplex, rational, range iterators, generic integers, and more!\n"
  documentation = "http://rust-num.github.io/num"
  homepage = "https://github.com/rust-num/num"
  -keywords = ["mathematics", "numerics"]
  +keywords = ["mathematics", "numerics", "bignum"]
  +categories = [ "algorithms", "data-structures", "science", "cryptography" ]
  license = "MIT/Apache-2.0"
  repository = "https://github.com/rust-num/num"
  name = "num"
  