digitallinguistics/spec: v0.21.1

This is a patch release with several hotfixes, and numerous updates to the project documentation and schema descriptions. Notable Changes A new developer readme! FIX: value of "main" in package.json FIX: allow negative values for Reference.year (#181) FIX: Text.contributors now references the Person schema instead of the non-existent Contributor schema (#118) FIX: Text.genre is now a standalone schema instead of referencing the non-existent Genre schema (#172) REMOVE: Text.status (#117) General SCHEMAS: reorder properties in schemas more logically (#151) FIX: value of "main" in package.json FIX: incorrect media types for schemas in Azure Storage (#154) FIX: update schema versions from commit https://github.com/digitallinguistics/spec/commit/cc8bac3af2087bf2975709e242a6ff2e460b43e2 (#175) DOCS: move project documentation to /.github folder (except README.md, which is needed in the project root for npm) (#127) DOCS: change LICENSE > LICENSE.md (#127) DOCS: point Code of Conduct to general DLx one (#160) DOCS: remove references to Slack channel (#127) DOCS: add developer readme (closes #143) DOCS: move user readme to /.github folder (#143) DOCS: add paragraph about Austin Principles to user readme (#124) DOCS: add TOC to user readme (#127) DOCS: add pull request template (#157) DOCS: add section to CONTRIBUTING.md on GitHub Flow / Branching Model (#127) DOCS: improve the introductory paragraph of user readme (#127) DOCS: fix broken links in user readme (#159, #168) DOCS: update testing guidelines in CONTRIBUTING.md DOCS: lowercase "object" when referring to a schema DOCS: update CONTRIBUTING.md with info about empty optional properties (cf. #173) DOCS: update PR template with reminder about schema versions DEV: convert YAML files before running tests or upload script DEV: don't overwrite existing versions of files in Azure Storage (#176) DEV: remove extraneous log statements from upload script Media FIX: capitalization of MultiLangString Reference FIX: allow negative values for Reference.year (#181) Text CHANGE: clarify that Text.contributors includes speakers (#119) FIX: Text.contributors now references the Person schema instead of the non-existent Contributor schema (#118) FIX: Text.genre is now a standalone schema instead of referencing the non-existent Genre schema (#172) REMOVE: Text.status (#117