Ignore two failing flatpipes tests
Move `position` and `rposition` methods to `ImmutableVector` trait
libstd: impl Num for BigUint/BigInt
libstd: impl `Orderable` for `BigUint`/`BigInt`
libstd: `Rational` requires `Integer` as type bounds instead of `Num`
libstd: `Ratio` requires `Clone` instead of `Copy`

This allows creating `Ratio<T>` which `T` is non-implicitly copyable types
such as `BigInt`.
libstd: Add tests for BigRational
Rename vec::len(var) to var.len()