Update LTLI

[aphillips]

• Make document consistent with Note status by removing contents about "normative"
• Added local.css (copied from string-meta)
• Coped string-meta's best practices note
• Styled, organized, and extended the best practices
• Added definitions for valid and well-formed
• Fixed my attribution
• Fixed respec errors and made references us https
• Moved the language tag terminology section under the I18N terminology section
• A few other edits to abstract, introduction

This is the first in what is expected to be a series of edits to bring this document up to Note status.

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[aphillips]

Note: Felix (@fsasaki) isn't listed on this repo still. @r12a or @xfq can you add him to reviewers?

[xfq]

Note: Felix (@fsasaki) isn't listed on this repo still. @r12a or @xfq can you add him to reviewers?

Done.

(BTW, I have resolved the merge conflict introduced by #5.)

[aphillips]

Given all the changes, I'm going to merge this PR.