fix: use absolute URL for demo GIF in Marketplace README

chore: prepare v0.5.2 release

- Copy LICENSE, CHANGELOG.md, THIRD_PARTY_NOTICES.md into extension dir during release
- Add copied files to .gitignore

Merge branch 'development'

Merge pull request #94 from ktmage/development

Release v0.4.2

Merge pull request #90 from ktmage/development

Release v0.4.1

Merge pull request #85 from ktmage/development

Release v0.4.0

Merge pull request #64 from ktmage/development

v0.3.0 リリース

Merge pull request #39 from ktmage/development

v0.2.0 リリース

fix: add --skip-duplicate to vsce publish