Archive repository

[ralphtheninja]

• [x] Disable Greenkeeper
• [x] Make sure the latest published version is git-tagged
• [x] Add note to readme (example: https://github.com/Level/level-mobile/pull/22)
• [x] Remove project from Travis
• [x] Pin dependencies
• [ ] Ask for npm ownership
• [ ] Release a final patch version
• [ ] Deprecate the package with This project has been abandoned. There will be no further releases. If you wish to revive leveldown-mobile, please open an issue (https://github.com/Level/community) to discuss a way forward. Thank you!
• [x] ~~Remove extraneous npm owners~~
• [x] Archive the GitHub repository