Lints to ensure link text for EIPs should match the EIP's number

Let's create two lints:

## `markdown-link-eip`

If the link destination matches the pattern `eip-([^.]*)\.md$`, trigger if the link text does not match `^(EIP|ERC)-\1$`, where `\1` is the proposal's number from the file name (aka capture group 1.)

For example:

* `[EIP-1](./eip-2.md)`
* `[EIP-1: Foo](./eip-1.md)`
* `[Another Proposal](./eip-1.md)`

If the link destination matches the pattern `eip-([^.]*)\.md#.+$`, trigger if the link text does not match `^(EIP|ERC)-\1\s*\S+`, where `\1` is the proposal's number from the file name (aka capture group 1.) Note that this pattern allows trailing characters.

For example:

* `[EIP-1](./eip-1.md#motivation)`
* `[EIP-2: Hello](./eip-1.md#abstract)`
* `[Another Proposal](./eip-1.md#rationale)`

## `markdown-link-other`

If the link text begins with EIP or ERC, the link target must be an EIP. For example:

* `[EIP-2](../assets/eip-2/foo.txt)`