Fix linkcheck errors

[niksirbi]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

Linkcheck was failing across dozens of links, blocking CI for in-progress PRs.

What does this PR do?

Deals with all the broken links via one of 3 strategies:

1. Most broken links were due to GIN. Here I chose to completely linkcheck-ignore GIN as it's often flaky (frequently goes offline)
2. A few broken links were leading to journal manuscripts. I replaced those with their permanent doi identifier links (which will not break), manually verified that the updated links resolve, and then added doi.org to the linkcheck ignore list (access to doi links is usually rate limited or completely blocked).
3. Some links (mostly to documentation sites) had genuinely changed and I updated those to new targets. I could no longer find the documentation site for SpikeForest, so I chose to link to the GitHub repo in that case.

References

Unblocks #81 and #80

How has this PR been tested?

Local linckheck run, CI, and manually checking the links from categories 2 and 3 above.

Is this a breaking change?

No.

Does this PR require an update to the documentation?

N/A

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[adamltyson]

LGTM, just a few suggestions.