Broken links from https://celestiaorg.github.io/celestia-app/

[rootulp]

Problem

1. Navigate to https://celestiaorg.github.io/celestia-app/
2. The links in the main page are broken but the links on the sidebar work

For example: https://celestiaorg.github.io/celestia-app/data_structures.html is broken but https://celestiaorg.github.io/celestia-app/specs/data_structures.html works.

Proposal

Fix the links in the main section. I think this may be resolvable by redirecting from https://celestiaorg.github.io/celestia-app/ to https://celestiaorg.github.io/celestia-app/specs/index.html

[rootulp]

IMO it doesn't make sense to nest most of the pages under 1. Specification. We can fix all the links and clean up the structure of the specs by removing the Specification item and moving all the nested pages one level up.