Clarifies that test cases shouldn't be external links. (ethereum#3250)

We have been enforcing this for a while, I didn't realize EIP-1 said something different.

EIPS/eip-1.md

@@ -102,7 +102,7 @@ Each EIP should have the following parts:
 - Specification - The technical specification should describe the syntax and semantics of any new feature. The specification should be detailed enough to allow competing, interoperable implementations for any of the current Ethereum platforms (cpp-ethereum, go-ethereum, parity, ethereumJ, ethereumjs-lib, [and others](https://github.com/ethereum/wiki/wiki/Clients).
 - Rationale - The rationale fleshes out the specification by describing what motivated the design and why particular design decisions were made. It should describe alternate designs that were considered and related work, e.g. how the feature is supported in other languages. The rationale may also provide evidence of consensus within the community, and should discuss important objections or concerns raised during discussion.
 - Backwards Compatibility - All EIPs that introduce backwards incompatibilities must include a section describing these incompatibilities and their severity. The EIP must explain how the author proposes to deal with these incompatibilities. EIP submissions without a sufficient backwards compatibility treatise may be rejected outright.
-- Test Cases - Test cases for an implementation are mandatory for EIPs that are affecting consensus changes. Other EIPs can choose to include links to test cases if applicable.
+- Test Cases - Test cases for an implementation are mandatory for EIPs that are affecting consensus changes. Tests should either be inlined in the EIP as data (such as input/expected output pairs, or included in `../assets/eip-###/<filename>`.
 - Reference Implementation - An optional section that contains a reference/example implementation that people can use to assist in understanding or implementing this specification.
 - Security Considerations - All EIPs must contain a section that discusses the security implications/considerations relevant to the proposed change. Include information that might be important for security discussions, surfaces risks and can be used throughout the life-cycle of the proposal. E.g. include security-relevant design decisions, concerns, important discussions, implementation-specific guidance and pitfalls, an outline of threats and risks and how they are being addressed. EIP submissions missing the "Security Considerations" section will be rejected. An EIP cannot proceed to status "Final" without a Security Considerations discussion deemed sufficient by the reviewers.
 - Copyright Waiver - All EIPs must be in the public domain. See the bottom of this EIP for an example copyright waiver.