Deprecate old modules

[vweevers]

Ref: How do I upgrade to abstract-level?

First let's do a doc-deprecation (too many downloads still):

• [x] memdown
• [x] level-mem
• [x] abstract-leveldown
• [x] level-js
• [x] levelup
• [x] leveldown
• [x] deferred-leveldown
• [x] encoding-down
• [x] level-codec
• [ ] multileveldown
• [ ] level-party
• [ ] subleveldown
• [x] level-errors
• [x] level-packager
• [x] level-concat-iterator
• [ ] level-test (TBD)
• [ ] rocksdb
• [ ] level-rocksdb

Then npm deprecation and archival of repo:

• [ ] memdown
• [ ] level-mem
• [ ] abstract-leveldown
• [ ] level-js
• [ ] levelup
• [ ] leveldown
• [ ] deferred-leveldown
• [ ] encoding-down
• [ ] level-codec
• [ ] multileveldown
• [ ] level-party
• [ ] subleveldown
• [ ] level-errors
• [ ] level-packager
• [ ] level-concat-iterator
• [ ] level-test (TBD)
• [ ] rocksdb
• [ ] level-rocksdb