Keep the subpage when going to latest version

[jyn514]

Addresses #200

If the page does not exist on the latest version, searches for a page with that title.

~~TODO: If

1. Going to a new version that
2. Deleted the existing module/item and
3. The user is looking at a platform other than the default,
   then the link will be wrong (it will not include the name of the crate).~~

The solution is to check if req_path[3] is the crate name or the platform. Once this is done, #200 (comment) will be trivial to fix.

This is fixed, see below.

[jyn514]

Also I haven't found a test case for an item that was deleted/moved between versions, if anyone knows of one please let me know!

[jyn514]

Fixed the bug with a different platform. I've tested the following manually:

• same item
• same item with platform
• renamed item
• renamed item with platform
• deleted item
• deleted item with platform

If anyone has suggestions for how to set up unit tests, I'd be happy to hear them! I'm not sure how to ensure that certain crates exist in the database :/

[jyn514]

This does not address the following issues:

• clicking the name of the crate in the top-left does not keep the platform
• choosing a different platform goes to the root, not to the current item

[jyn514]

This is ready for review.

[EverlastingBugstopper]

This is fantastic, thanks so much @jyn514

[QuietMisdreavus]

Thanks so much! This is really great functionality for the site, and no doubt it's one of the more requested features we've had. I just have a couple of nits about comments, but otherwise this looks great!

[jyn514]

Added comments as requested :)

Thanks for taking a look at this!

[QuietMisdreavus]

Thanks so much! Let's get this merged.

[daboross]

Thanks for doing this!