terraform-provider-null-3.0.0-6.3.1

- Add symbolic link to comply with new filesystem layout for local provider copies
- Define and use common Go spec file variables

- Update to version 3.0.0:
  * add .tfproto5 file for releases
  * Update CHANGELOG.md
  * Update CHANGELOG.md
  * update go version in go.mod
  * normalise naming conventions
  * Add descriptions
  * update CI
  * SDK v2.0.3
  * update provider directory layout
  * force go modules on for travis
  * restore hashibot behaviors post migration
  * Update CHANGELOG.md
  * switch to standalone sdk
  * bump terraform to v0.12.8
  * Cleanup after v2.1.2 release
  * Fix typo in resource.html.markdown

- spec-cleaner run

- Setup as service
- Brush up spec file to reduce distro branching
- Create symlink for recognition by terraform

- Initial packaging of the null provider