Extracts redirect matching logic to its own match_redirect method.

[nicholasio]

Description of the Change

Introduces a new match_redirect method and updates maybe_redirect to use this new method.

It also introduces a srm_match_redirect function to expose matching redirect logic to themes and plugins.

Alternate Designs

See #197

Benefits

Code is more testable now and maybe_redirect now only does one thing.

Possible Drawbacks

None

Verification Process

Manual testing

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry

[jeffpaul]

@nicholasio thanks for the PR, it's greatly appreciated! I've pinged @tlovett1 for review on this in planning for getting it into our next milestoned release, so stay tuned for any feedback from that review.

[dinhtungdu]

LGTM 👍

Edit: This is just my preference, but if we return early in maybe_redirect method, we can save one level of indentation:

if ( empty(  $matched_redirect ) ) {
    return;
}

// Do the rest
...

[nicholasio]

@dinhtungdu done, that is generally my preference as well.

[dinhtungdu]

🎉