digitallinguistics/spec: v0.21.1

This is a patch release with several hotfixes, and numerous updates to the project documentation and schema descriptions.

• 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)

• 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

• FIX: capitalization of MultiLangString

• FIX: allow negative values for Reference.year (#181)

• 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)