EncodeLike<Self> should be implemented for all Encode types

in this context:

fn foo<T: Encode>(t: T) {
    put<T, _>(t);
}

fn put<T, EncodeLikeT: EncodeLike<T>>(like_t: EncodeLikeT) {}

this doesn't work because T doesn't implement EncodeLike, only Encode.
A way to solve this would be to have the following traits:

pub trait Encode: EncodeImpl + EncodeLike {}
impl<S: EncodeImpl + EncodeLike> Encode for S {}

and rename Encode -> EncodeImpl

but this is a breaking change. Actually maybe we may be able to change it without breaking substrate by first releasing new minor of version of parity-common/primitive-types with EncodeLike impls

Start by locating the Encode, EncodeImpl, and EncodeLike trait definitions and their implementations in this Rust crate. Review compatibility with parity-common/primitive-types and the existing test suite; done means a decided, non-breaking path for making Encode values usable where EncodeLike is required.