Fix docs source links

[JSap0914]

Summary

• update docs and package source links that pointed at the missing v0.1.0 Git tag
• point the conformance discussion link at the existing guides/conformance.md document
• set ExDoc source links to main so generated docs do not emit broken v0.1.0 source URLs

Fixes #1.

Verification

• old reported guide URL: HTTP 404 for https://github.com/elixir-localize/localize_person_names/blob/v0.1.0/guides/integrating_existing_structs.md
• new guide URL: HTTP 200 for https://github.com/elixir-localize/localize_person_names/blob/main/guides/integrating_existing_structs.md
• checked all changed main GitHub source URLs: HTTP 200
• git diff HEAD~1..HEAD --check
• rg confirmed no remaining blob/v0.1.0 or specification_deviances.md references in README.md, guides, or mix.exs

Note: mix is not installed in my local environment, so I could not run mix docs here.

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