Update design doc for message pattern quoting (#503)

* typo

* Contextualize templating libraries

* Differentiate template rules from output format rules, give examples of whitespace handling rules for template languages

* Update containing format escape rules interaction and assumptions about frequency

* Move usage stats from Background to Use Cases, contextualize frequency vs. importance vs. i18n best practices

* De-emphasize overstated developer-only concern

* Fix design tenet wording using quotes from noteworthy prior art

* Update rest of Requirements

* Update Constraints

* Remove duplicate section not properly deleted after copied for a move

* Update Design area (proposed, alternatives, simple message consensus)

* Update title and objective to reflect focus of discussion

* Wordsmithing and formatting

* Update contributors list

* Apply suggestions from code review

Co-authored-by: Addison Phillips <[email protected]>

* Apply suggestions from code review

* Rewrite largely based on PR #504; keep priorities, non-reqs, prev info

* Useful addition

Co-authored-by: Eemeli Aro <[email protected]>

* Update exploration/text-vs-code.md

Co-authored-by: Eemeli Aro <[email protected]>

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Co-authored-by: Addison Phillips <[email protected]>
Co-authored-by: Eemeli Aro <[email protected]>