[manifest] Fixed up titles and dfns (#393)

Removes Respec warnings about abusing title attributes. Cleans up markup. No normative changes. 
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/manifest/pull/393

-- Commit Summary --

  * Fixed up titles and dfns

-- File Changes --

    M index.html (373)

-- Patch Links --

https://github.com/w3c/manifest/pull/393.patch
https://github.com/w3c/manifest/pull/393.diff

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/pull/393